KD6 (I-168) class submersible (1933)

IJN Large oceanic submarines 1934-45.
KD VIa (Kaidai-roku-gata-ē, I-68/I-168-class): I-68, I-69, I-70, I-71, I-72, I-73, renamed +1 1942
KD VIb (Kaidai-roku-gata-bī, I-74/I-174-class): I-74, I-75, renamed +1 1942

The Kaidai VI type (“Navy large type VI”) or I-68-class (海大5型) Kaidai-go-gata, Project number S31, for the KD VIa six boats I-68-70 all completed in 1937 and for the two VIb, (Project S34), in 1938 for ten submarines total. The design was the result of tweaking the standard displacement to match the new London Treaty limits at 1,400 tonnes, but in reality they were longer than the KD-V, had better diesels,; greater speed, and more range. The KD VIb were virtually identical, albeit they displaced more, and had a better 120 mm gun, extra range, dived deeper, and had a new hydrophone type. They started their career with the war in China from 1937 and took part in the Pacific War: One was lost in an accident, and all were sunk in action but I-168 famously sank the USS Yorktown at the tail end of the Battle of Midway. Others took part in the Pearl harbour attack, and two were converted as Kaiten transports to the end of the war.

Development of the Kaidai VI

Hirootoko’s Colorization of the I-71 on trials in Kobe December 1935.

The Kaichū Type were the standard IJN cruiser submarines, but they did not carried on board seaplane (apart tests made on earlier types). They derived from 1918 German “U-kreuzer” like the U-142 class, and from later unbuilt models which plans were obtained as war reparation after 1918. This allowed Japanese engineers to create their own original long range design of long range fleet submarines. In the 1920s the KD1, KD2 were not very successful but enabled to start a lineage from 1919 that was incrementally improved. The KD3 was a reliable fleet operation and reconnaissance baseline for the KV IV and V, all with high surface speed, very long range, heavy armament for fleet operations.

The London Treaty Tricks

The Kaidai 6 were extrapolated from Project 29 (Kaidai V), were planned under the 1930 (Showa 5) fiscal year program and 1st Naval Armaments Supplement Programme (Maru 1), under design designation S31. The great game changer was indeed the London Naval Conference, that Japan signed, and which forced alteration to the design, due to their more restrictive clauses on large submarines, so their standard displacement was limited to 1,400 tons. For these six VIa submarines, completion ranged from 1932 to 1937. As a reminder, the previous KD V displaced more than 1,570 tonnes surfaced and c1,700 surfaced, normally fully loaded. Going from 1,570 to 1,400 tonnes standard or unloaded while keeping the same characteristics proved a gamble for Japanese engineers. But instead of finding ways and compromises, the numbers declared were just falsified.
The 1930 London treaty provisions on submarines indeed had a displacement Cap for new submarines that could not exceed 2,000 tons standard displacement, not 1,400 which was the Japanese interpretation. There was a Loophole Exception to retain or acquire a maximum of three large submarines up to 2,800 tons for France with Surcouf for example. The 1400 tonnes limit was rather based on the Japanese total Tonnage Cap capped at 52,700 tons.
International engineers that looked at the design and saw the new boats were in fact several meters longer for the same beam concluded there was no way to declare a 170 tonnes lower displacement.
If anything they were at least 100 tonnes heavier. If inspected closely however, there was a listing of equipments and loads usually listed as present on the boat to calculate the standard displacement, and they were just omitted. Other were declared underweight. It was argued they would simply be refitted “in case of war”. By playing with the rules, and possibly falsifying yard’s hull calculations, then all internal items calculations, it was then possible to present inspectors a net balance of 1,400 tonnes. This spared 600 tonnes over the 2,000 tonnes cap that could be used to built more submarines down the line. One such “trick” also would be the new diesels, supposedly lighter, yet more powerful than the previous ones, and a more clever way to integrate ballasts and fuel tanks between the pressure and outer hull to obtain a large fuel capacity as well (see below). However even the pressure hull was increased in thickness on the next KD 6b design.

Because at the end of the day, they had a fully loaded displacement superior by some 85 tonnes compared to the Kaidai 5. In fact when submerged and fully loaded they reached a calculated 2,440 tonnes versus 2,330 tonnes on the KD 5. The KD 6b were even heavier. With the KD 7 approved in the 1939 program, the very last Kaidai (10 built) since this was post-1936, the Japanese had ripped off the treaties, and were at war from 1937 anyway. So they ended at 1630 tonnes standard, close to 2610 tonnes fully loaded and submerged.

Better Speed and Range

The powerplant was to be brand new, the “Navy Headquarters” designed diesels delivering approx. 1.5 times the output of the previous “Zu-shiki No. 3” model of the previous KD V, which, together with a reducution of weight and size, promised exceptional performances. The navy was promises these new submarines would be able to achieve speeds up to 23 knots. This ambitious target, set for the Kaidai from the very beginning, would have made them the world’s fastest submarines. However, as the class was built and tested, the engines proved utterly unreliable in their early life, and the issues were not fully resolved until around 1938. Fuel capacity was increased given the extra size, by approximately 100 tons, so the cruising range ended about 40% greater than that of earlier Kaidai-class.
As for the armament, the first three, I-68, I-69, and I-70 had the same 10 cm high-angle dual purpose guns (A/S and AA) while the remaining three I-71, I-72, and I-73 were instead refitted with single 12 cm guns. AA and torpedo specifications remained largely identical to the Kaidai Type V.

The Kaidai VIa and b changes in a nutshell

The Kaidai VI approved in the 1931 programme were laid down in 1932-34, launched 1933-35 and completed, for the last one, in 1937, the same year Japan launched its own war on China. Despite the lower standard tonnage declared, they were in reality longer and displaced 110t+ more when fully loaded and submerged. After the six submarines of this group, from I-68 to I-73, a pair of extra KD VI was ordered as part of th 1934 programme, laid down in 1934-35, launched 1936-37 and completed in 1937-38.
These last two submarines were built under the Second Naval Armaments Replenishment Programme (“Maru 2” Plan) under design designation S34 since it was FY1934. While fundamentally identical to the preceding Kaidai VIa, the hull plating thickness was increased, raising the safe diving depth to 85 meters. Fuel capacity was increased by approximately 100 tons, further extending operational range. Like the last three vessels in class, they were armed with a 12 cm naval A/S gun and with the new Japanese Type 93 hydrophone.

They were virtually identical but with a declared standard displacement superior at 1,420 tonnes, large underwater, submerged displacement of some 110 tonnes, a bit more draught, fuel tanks enlarge, range was calculated at 10,000 nm but at 16 knots versus 14,000 nm at 10 knots so that their cruise speed to reach their objective was 6 knots faster. Translated to 10 knots lower cruise, that would be probably around 15,000 nm or more. Which was simply exceptional for the time. Thus, they had the same underwater range as the KD VIa and KD V. Extra space was also allocated to larger ammunition. Going from 100 mm DP gun to a 120 mm or 4.7 inches/45 naval A/S gun was seen as a return to the KD-4 design, to try to regain lethality in surface combat. AA was also reinforced, with four instead of just one heavy MG.

Design of the KD-VI class

The KD-6 as seen above were overall larger than the KD-5, while cheating on the standard displacement. Indeed, there was no way the new designed, larger overall, could do 1,400 tonnes standard versus 1,575 tonnes. That 175 tonnes differences was obtained by playing all the trick in the book, omitting “wartime” equipment, cheating on individual item’s weight, like the diesels, and large volumes of fuel, oil, food, water and playing around even with the crew itself, reduced from 70 down to 60 on paper. The average Japanese male body weight for a crew of 70 was 3,92 tonnes on average, based on census of that era giving a 54-58 kgs range, versus 3.3 tonnes for 60. But in wartime, it went from 82 to 84. As usual there was enough room between the flat deck of the outer hull and rounded top of the pressure hull below to store many items, including at least two inflatable life rafts and a rigid boat. The return on the 120mm caliber for the last three boats of the KD 6a and the two KD 6b were also an aknowledgement of the London Naval Treaty generous cap for submarine deck guns to 5.1 inches (130 mm). And those up to 6.1 inches or even 8 inches were only allowed to the few exempted oversized boats such as Surcouf.

Hull and general design

The KD-6a displaced 1,400 long tons (1,422 t) tonnes standard as seen above, for both batches and 1,420 long tons (1,443 t) surfaced for the Kaidai 6b, then 2,440 long tons (2,479 t) and 2,564 long tons (2,605 t) respectively for the KD 6a and KD 6b.
In size, they were longer than the KD 5, going from 97.70 m (320 ft 6 in) overall to 104.70 m (343 ft 6 in) on the KD6a and even 105 m (344 ft 6 in) on the KD 6b.
In Beam they were identical at 8.20 m (26 ft 11 in) for all variants.
In draft they went from 4.70 m (15 ft 5 in) down to 4.58 m (15 ft) or 4.60 m (15 ft 1 in) on the KD 6b and they had a moleded depth of 7.05 m (23 ft 2 in) of the KD 5, 7.00 m (23 ft) on both the KD 6a and 6b.
The general outlook was about the same as well. Underwater, they had the samel fuller form as the KD 5, with a rounded stem with the traditional net cutting teeth on the jaw, but no systematic upper gimble net cutting saw, albeit some seees to sport it. They had recesses anchors, same type as before, a pair of forward overwater rounded diving planes, fixed (not retractable) but short and protected above by guard bars. The keel was straight and long, with a step and a sloped end to the tail assembly. The two short drive shafts were protected by generous aft guard bars.

The aft dive planes were squared, as the main rudder. There was also, an inheritance of german designs, a surfaced rudder. The prow was lightly taller than the deck level, with a raised foredeck but rounded, as the outer hull,and the flat-sided outer fkat deck merdged into the forward and aft hull. There was only a single deck hatch, located aft port. There was a main torpedo loading hatch forward, preceded by a crane that could be folded down for underwater travel and reduce drag, and same aft, but close to the conning tower. The latter had the same overall design as previous KD V boats, with a “shoe” at its step, topped by a small projector remotelly manned from the windowed bridge at the front of the fairing.

It also integrated the helmsman post and ran all the way to the conning tower countaining the two periscopes, attack and watch and the frame portico supporting wireless radio cables. The main gun was located on a slightly taised portion of the deck forward of the CT, protected by a wave breaker. The wireless radio cables were hanging from a single forward telescopic mast, tow to the portico. There was also a telescopic signal mast. The aft flag mast however was fixed. There was a forward capstan and several pairs of bollards fore and aft for berthing operations. The deck was covered for most its lenght by pine wood planking. The interstices on the “cigarette deck” allowed water to pour in when diving. As usual the hull was also dotted with several series of water scoops. There were some detailed changes compared to the KD 5 for faster filling, with top and bottom scoop lines forward notably.

Powerplant

The great novelty of the design resulted in their brand new diesels: Instead of the previous Sulzer Mk.3 diesels they had Kampon Mk.1A Model 8 diesels, still mated on 2 shafts with the same standardized 3-bladed propellers. They remained the same on the KD 6a and b and produced 9,000 bhp versus 6.800 bhp on the KD 5, making for a speed gain of 2.5 knots from 20.5 knots (38.0 km/h) to 23 knots (42.6 km/h). It must be stressed that this was exceptional for the time. US Submarine of the time like the Tambor, Sargo and Salmon-class had a surface top speed of 21 knots (39 km/h), submerged speed of about 8.75 to 9 knots based on the same electric engines and batteries as before. The submarines carried more fuel as seen above, from 230 to 341 tons, and this made for a range of 14,000 nmi (26,000 km) at 10 knots (19 km/h) versus 10,000 nm on the KD 5. The KD 6b had a further increased fuel storage at 442 tonnes to reach 10,000 nmi (19,000 km), but at 16 knots (30 km/h), meaning perhaps 15-16K nmi at 10 knots. The KD 6a had almost the same underwater range as the KD 5 at 65 nmi (120 km) at 3 knots (5.6 km/h) versus 60 nm, but the KD 6 had an increase battery capacity for a range of 90 nmi (170 km) at 3 knots (5.6 km/h).
The KD 6a could dive at 70 m (229.7 ft), less than the KD 5 (75.0 m /246.1 ft). However the KD6b had an increased pressure hull thickness in order to now reach 85.0 m (278.9 ft).

Armament

I-68 and sisters of the KD-VIa and b retained the same armament as the previous KD-5, six 533mm torpedo tubes, four forward, and two aft (and 14 total, so 8 in storage). But there were differences withing the KD 6a class: The first batch of three counted much on the same 100mm/60 (4″) dual-purpose deck gun for most of her antiship work. It lacked punch due to a smaller HE shell, albeit this was compensated for a much greater muzzle velocity, but the second batch of three had instead a 120 mm/45 as previous Kaidai classes, and so were the KD 6b.

100cm/50 Type 88 deck gun (KD6a 1st batch)

The 10 cm/50 Type 88 naval gun was a dual-purpose model that existed in two variants:
-One variant had a removable barrel liner
-The other had an autofretted monoblock barrel.
Both variants had horizontal sliding block breaches, hydro-pneumatic recoil mechanism, Fixed Quick Fire ammunition. They were mounted on HA/LA central pivot mountswith up to 90° elevation. The theoretical rate of fire of 12 rounds per minute was limited to half this due to the speed of the pneumatic shell hoist (and training). This was the shining uniquely new deck gun aboard I-165 class Type KD5 submarines of the Imperial Japanese Navy. It was never used on other subs.
Specs:
Mass 2,830 kg (6,240 lb), length 5.3 m (17 ft 5 in), barrel 5 m (16 ft 5 in)
Shell: Fixed Quick Fire 100 mm x 380 mm 13 kg (29 lb) 100 mm (3.9 in)
Breech: Horizontal sliding block, recoil Hydro-pneumatic. Central Pivot mount -7° to +90°, 2×150° traverse
Muzzle velocity 885–895 m/s (2,900–2,940 ft/s), efective range 11,200 m (36,700 ft) at +90°, max 16.2 km (10 mi) at +45°. 1

120cm/40 Type 89 deck gun (KD6a 2nd batch, KD6b)

The 120 mm (4.7 in) L/40 11th Year Type was a 1922 redesign of the earlier 12 cm/45 3rd Year Type, built-up gun with central rifled tube and reinforcing tube layers. Depending on sources the barrel was noted either at 40 or 45 calibers. The ring cradle was on a pedestal mount with an hydro-pneumatic recoil mechanism, with a main cylinder below the barrel and two on top. It had a horizontal sliding-block breech and fired separate loading cased charges and projectiles and had a wider range of elevation and traverse at +55° but too heavy and dlow to be considered a dual-purpose gun by any margin instead of the 100 mm/50 Type 88.
Mass: 3,250 kg (7,170 lb), Length 5.26 m (17 ft 3 in), barrel 4.42 m (14 ft 6 in), Height 2.1 m (7 ft).
Separate loading 120 x 550R cased charges and projectiles, 44 lb 12 oz (20.3 kg)
Rate of fire: 5-6 rounds per minute, Muzzle velocity: 2,700 ft/s (820 m/s)
Effective firing range: 17,500 yd (16,000 m) at 33°
Ammunitions: Common Type 0 45 lb (20 kg), Type 1 45 lb (20 kg), ASW 1a: 36 lb 5 oz (16.5 kg), Illumination 2a 45 lb (20 kg).

Type 89 533mm Torpedo

The KD-VI had four tubes in the bow and reloads for each, plus two in the stern and two reloads, for fourteen total of the 89th Year Type torpedoes. This model was designed from the Type 8 at the Imperial Japanese Navy Technical Department. Design Year: 1929 (entered service in 1931; named for Imperial Year 2589). Introduced in 1931, it became the new standard to replace the 1914 Type 8, was widely used by early-war Japanese submarines.

Specifications:

Diameter: 53.3 cm (21 inches)
Propulsion: Two-cylinder, double-acting horizontal engine (very reliable design influencing subsequent Japanese wet-heater torpedoes).
Speed & Range: Maximum speed of 45 knots with a range of approximately 5,500 meters.
Warhead: Heavy explosive charge (roughly 300 kg/660 lbs depending on the variant fill like Shimose or Type 97).

Type 92 Heavy machine gun

In the rear part of the fairing and platform was a single Type 92, 12 mm (0.48 in) heavy MG, the same used by the Army. It was a hefty beast 55.3 kg (122 lb) without the mount and needed 2-3 men to have it unpacked and installed when surfaced. It measured 1,156 mm (45.5 in) for a barrel length of 721 mm (28.4 in) and firing a cartridge 7.7×58mm Type 92. Gas-operated the rate of fire was 450–500 rounds per min for a muzzle velocity of 780 m/s (2,600 ft/s). Effective firing range however was only good against low (flying strafing aircraft back in 1930, at 800 m (870 yd) for a maximum firing range of 4,500 m (4,900 yd). The Feed system comprised 30-round Hotchkiss-type metal strip.
Indeed, this machine gun was historically a scaled-up version of the Type 3 heavy machine gun, calibre 7.7 mm, air cooled, ammo strip-fed, based in turn on the Hotchkiss M1914. The air cooling imposed a series of metal rings. It was coupled with a ring-type anti-aircraft sight as well.
The KD VIa was supposed to have like the previous KD V, a single one aft of the CT plus a pintle-mounted optional 7.7 mm Type 92. This was recoignized as poor and the next KD VIb had instead four 13.2 mm Type 92 HMGs, as noted in conways, likely in two twin mounts, but it is not confirmed in all sources.

Sensors

These KD-V and VIa had a pair of hydrophones of the MV-Chubu type echo-sounder, a ratio transmitter special 4 and 2 receiver RDF-T4. They also had degaussing equipment with three 3/8 inch coils directly below deck and two fitted on the sail like her sister. The KD VIb had the new Type 98 Hydrophones: The (98式集音器 or Kyūjūhachi-shiki Shūonki) was athe new standard passive sonar system deployed by the Imperial Japanese Navy (IJN), relying on sensitive underwater microphones listening for the engine vibration and propeller sounds. It was installed as an array of sensors mounted flush to or along the hull of the vessel. They could capture raw acoustic pressure, not measure exact distance instantly. Operators used the time-delay of sound hitting different parts of the array to triangulate an incredibly accurate bearing (direction) toward the target. The Type 98 operated effectively across low-frequency spectrums. Because low-frequency waves travel much farther through water without losing energy, these hydrophones could often detect surface convoys dozens of miles away under ideal thermal conditions.

Author’s profile

⚙ I-68 (KD 6a) specifications
Displacement	1,400 long tons surfaced, 1785t normal, 2,440 tons submerged, fully loaded
Dimensions	104.70 x 8.2 x 4.57m (343 ft 6 in, 26 ft 11 in, 15 ft)
Propulsion	2x Kampon Admiralty diesels: 9,000 bhp surfaced. 2 EM, 1,800 shp submerged
Speed	23 knots surfaced (42.6 kph), 8.2 knots (15.2 kph) submerged
Range	341 tons fuel, 14,000 nm/10 kts surfaced, 65 nm/3 kts submerged
Armament	6× 533 mm TTs (4 bow, 2 stern, 14), 1x 100 mm/50 DP deck gun*, 1x 12mm Type 92 HMG AA.
Test depth	70 m (229 ft)
Sensors	MV type Hydrophones
Crew	68

⚙ I-74 (KD 6b) specifications
Displacement	1,420 long tons surfaced, 1810t normal, 2,564 tons submerged, fully loaded
Dimensions	105 x 8.2 x 4.6m (344 ft 6 in, 26 ft 11 in, 15 ft 1 in)
Range	442 tons fuel, 10,000 nm/16 kts surfaced, 90 nm/3 kts submerged
Armament	6× 533 mm TTs (4 bow, 2 stern, 14), 1x 120 mm/40 deck gun, 1-4x 12mm Type 92 HMG AA.
Test depth	85m (279 ft)
Sensors	Type 98 Hydrophones
Crew	68

Gallery

A view taken from the Japanese submarine I-70 by Technical Lieutenant Commander Hori Motomi at their work site in Ariake Bay. From the front are the submarines I-68 and I-69 submarines, and the light cruiser in the background is the squadron flagship Kinu. The aircraft carrier visible in the distance is marked “Kaga.” March 1936

The Japanese submarines I-168 and I-169 on training duty, 1936

The Japanese submarines I-172, I-171, and I-173 on patrol duty Date 1941

I-70 underway

I-73 1939 April 24.

Career of the KD-VI class

I-68/168 (1933)

Lead boat of the early batch KD VIa, she was laid down at the Kure Naval Arsenal on 18 June 1931, launched on 26 June 1933 and commissioned on 31 July 1934. She is the one also with the greatest photo douomentation in open source as the press took place onboard at some point for a documentary at the time. Upon commissioning, she was attached to the Kure Naval District and joined the newly formed Submarine Division 12, deactivated in 1929 but reactivated on 8 October 1934, joined by I-69. Their unit was subordinated to Submarine Squadron 2, 2nd Fleet (Combined Fleet) from 15 November 1935. On 13 April 1936 she left Fukuoka with sisters I-69 and I-70 of batch 1 for a training cruise off China-Qingdao and bacl to Sasebo on 22 April. They left Mako (Pescadores) on 4 August 1936 for a training cruise in the Amoy arean back on 6 September. Their unit entered the 3rd Reserve, Kure Naval District on 15 December 1938, then under direct command from May 1939. The unit joined Submarine Squadron 3, 2nd Fleet from 15 November. I-68 left Okinawa on 27 March 1940 with I-69, I-70, I-73, I-74, I-75 to train in southern Chinese waters and arrived at Takao, Formosa (Taiwan), on 2 April. On 11 October she took part in the Yokohama Bay Imperial fleet review, largest in Japanese history for the 2,600th anniversary of Emperor Jimmu. She was decommissioned in reserve on 19 October, her unit realocatted to the 6th Fleet on 15 November and she was back in service by 25 July 1941.

By 11 November her unit was assigned to the 6th Fleet’s Advance Force (Vice Admiral Mitsumi Shimizu). He gathered all commanders on his flagship, IJN Katori with his chief of staff to expose Operation Z, the naval part of the attack on Pearl Harbor. I-68 departed Saeki Bay, Kyushu on 11 November 1941 with I-8, I-69, I-70, I-71, I-72, and I-73 for Kwajalein Atoll (20 November) and for her part in Operation Z, she left on 23 November for the Hawaiian Islands. En route, she received the message “Niitakayama nobore 1208” confirming the attack on 2 December. On 7 December 1941, all Submarine Squadron 3 was 25-50 nautical miles south of Oahu with. Their role was to ambush any warship, especially thos priceless battleship, trying to escape the harbour under heavy air attack. But they spotted none. On 8 December, I-68 and I-69 started the rescue of midget submarine crews but none returned. I-68 returned to her previous posision but spotted no target. However ASW patrols on the US side were considerable. Until 13 December 1941, she was subjected to no less than 21 separate depth-charge attacks, forced to crah dive each time she was spotted by air or ships. The last attack damaged her battery cells, flooded her aft torpedo tubes. Lieutenant Commander Otoji Nakamura decided to head for Kwajalein, reached on 28 December.

She had repairs at Kwajalein, and by 31 December proceeded to Kure (arrived 9 January 1942) to complete repair. Nakamura was ordered to the flagship IJN Yamato on 17 January 1942 to exposed to Admiral Isoroku Yamamoto and his staff how the US proceeded to their depth-charge attacks in Hawaiian waters. This led to doctrinal revisions and instructions sent to all commanders. On 31 January Lieutenant Commander Yahachi Tanabe took command. On 20 May she became I-168.
For her second patrol she was assigned to Operation MI, the planned invasion of Midway Atoll as one of 13 submarines in the Advance Expeditionary Force. She left Kure on 23 May for Kure Atoll, abour 50nm west-northwest of Midway, from 31 May and on 1-2 June 1942, she was on the northwest coast of Midway, staying three days to observe the area through her periscope by day, binoculars by night, only reporting patrol aircraft launches before the attack, so the surprise was seemingly lost. She recoignized the Island closer on 2 June. On 3-4 June she circumnavigated Midway for weather reports.

Japanese planned made a Japanese submarine patrol line, part of the Advance Expeditionary Force to intercept, at least visually passing by US carriers from their respective far apart patrol stations. But none made contact. On 4 June Akagi, Kaga, Hiryū, and Sōryū launched their attack on Midway Island, I-168 observed airstrikes. Later she was informed of the battle, the loss of three carriers on the Japanese side while USS Yorktown was also assumed sunk, so Yamamoto ordered I-168 to shell the airfield on the eastern Island in advance of the same by heavy cruisers at 01:00 on 5 June. She reported U.S. air activity and surfaced 4,500 yards (4,100 m) off the eastern tip at 21:54 on 4 June, proceeded to Sand Island and at 01:24 on 5 June opened fire from 1,100 yards (1,000 m) southwest of Midway, six rounds (no damage) but was forced to submerged with searchlights searching for her and coastal artillery starting to bark. Based on this, the heavy cruiser bombardment was cancelled.

On 5 June early hours Japanese floatplanes from IJN Chikuma spotted the crippled USS Yorktown some 150 nm (280 km) NE of Midway. Depending on sourve it’s possible that a PBY Catalina attacked I-168 while surfaced, before she was ordered to sink Yorktown after resurfacing, after the attack, or she was attacked prior. She sailed to the reported position, estimated the crippled carrier’s possible speed as an option but her lookouts eventually spotted her by night from 12 nautical miles (22 km) at 04:10 on 6 June so she closed the range down to 11 nautical miles (20 km; 13 mi) at 6 knots to prepare launching, when at 05:30 they also spotted the DD USS Hammann tied up along Yorktown′s starboard side for firefighting and assistance of the carrier under tow by USS Vireo. She also spotted other destroyers circling away at 06:00 so she submerged. She approached to 3 knots through the destroyer screen, remaining undetected. But to avoid using her periscope she went too close in her initial approach, so she made another pass, circling to starboard to increase range, then fired four Type 89 spaced by three seconds each around 13:30 from 1,200 yards (1,100 m) or 13:31 from 1,900 yards (1,700 m). At any rate, the first torpedo struck Hammann. Given its massive payload, the detonation blew open her machinery space and she flooded ramidly and sank four minutes later (81 down, many killed by her depth charges explosions). At 13:32 the 2nd and 3rd torpedoes struck the same starboard side of the carrier below the bridge, but the fourth missed astern.

I-168 now being “discovered” by this attack, dove to 200 feet (61 m) and passed directly under Yorktown despite the danger of the latter capsizing over her. Destroyers present mas a savage counterattack at 13:36. One passed direclty over I-168, dropped two depth charges and USS Gwin, Hughes, Monaghan dropped up to 60 more depth charges. I-168 was badly hit at 15:30 due to a severe hit at the bow, she operated with emergency lighting and the crew frantically tried to close the outer and inner hatches of No. 1 torpedo tube. The forward torpedo room and maneuvering room were flooded, and the forward battery room badly damaged, she was about 60 feet (18 m). The damaged forward battery cells release deadly chlorine so the crew had to put on gas masks. An evacuation to the aft compartment was decided, with the men grabbing rice sacks from the forward storage, sent astern to trim her and avoid her bottom to clear surface and everything they could find as ballast.
I-168 stayed there until the batteries were nearly exhausted. Despite the danger she surfaced at 16:40 just before sunset, with the crew prepared to man the guns.

She could observe USS Gwin, Hughes, and Monaghan just waiting 5 nautical miles (9.3 km; 5.8 mi) away. But I-168 remained undetected, so captain Nakamura decided to run away at 14 knots (26 km/h; 16 mph) both to charge batteries and ventilate as making distance until the cover of night. She reported later her sistuation to Combined Fleet HQ, claiming Yorktown sunk for good. Sources diverged on the fact I-168 was in fact spotted, caiufght and fired upon from 11,000 yards (10,000 m), herself replying from 6,500 yards (5,900 m) for 30 minutes another, or engaged from 5,470 yards (5,000 m). In between the crew completed emergency repairs to one electric motor so she submerged again, to redsurface at 20:00 after cashing in a new attack of 40 depth charges over 13 hours down under.

New emergency repairs done, I-168 managed to reach Japan on her diesels over twelve days, out of fuel when she entered Yokosuka on 19 June. She was then repaired for months at Kure. When she arrived news of her exploits had preceded her, there was a crowd, a band, and dignitaries made speeches. She was sent to Sasebo on 25/26 June 1942 for proper repairs. USS Yorktown eventually sank on 7 June. The crew battled flooding for more than a day. I-168 was praised as one of the only two Japanese submarines seeing action at the Midway and she sank the only 2 USN ships in this battle. The news reported that USS Yorktown was the largest warship sunk so far in the Pacific campaign only surpassed in 1944 by USS Archerfish with IJN Shinano.
Meanwhile the Guadalcanal campaign started on 7 August and I-168 departed Sasebo on 31 August for Truk, Carolines to support efforts in the campaign. She spent two months patrolling and was back at Kure on 18 November, drydocked for maintenance. She left Kure on 15 December for Truk (22ns) then the Shortland Islands, with 15 tons of cargo for the troops stranded at Guadalcanal, arrived on 1 January 1943 to unload 60% of her cargo before diving when two PT Boats arrived that night. She sailed back to the Shortlands for an overnight stop on 3–4 January, Truk 7-8 January, and Kure on 14 January.

While there her skipper received new orders: She was reassigned to the Northern District Force, the Aleutian Campaign, Attu and Kiska. She left on 22 February for Yokosuka until 5 March prprepared for the cold, supplied and then to Paramushiro, northern Kuril on 10 March, departed on the 13th for a supply run (ammunition) for Attu and Kiska garrison. Her first stop was at Holtz Bay, NE Attu on 15 March. She unloaded a first half and the remainder at Kiska. However as she proceeded into Holtz Bay at 17:27 she was spotted by USS S-32 laying in ambush. She fired three torpedoes and reported a muffled explosion. Her sonar operator noted no more propeller noises. In earlity she missed. I-168 was shadowed until 17:36, when she lost. I-168 arrived at Kiska on 17 March, unloaded the rest plus 6 tons of provisions and was ordered south of Amchitka. On 1 April she returned to Kiska, embarked sick personnel and some ground personnel from the 452nd Naval Air Group, and sailed to Paramushiro (arrived on 4 April).

I-168 left Paramushiro on 10 Aprilwith again a load of ammunition and mail to Attu and Kiska, arrived Attu on 12 April, unloaded, then Attu on 14-16 April again embarking staff officers and returned to Kiska, (19 April). She unloaded her cargo and arrived at Yokosuka on 9 May. After overhaul she departed for Kure and from there on 12 July Truk on the 22nd. Then Rabaul (New Britain/Bismarck Archipelago). But as she arrived at dusk on 27 July she transmitted her last routine report, somewhere in the Isabel Strait, her last.
It is now known from reports that on 27 July she spotted USS Scamp while surfaced in the Steffen Strait, near New Hanover Island. She closed undetected and fired a torpedo at Scamp. The latter spotted the incoming trail, ordered full ahead and crash dived, it missed; She went down to 220 feet (67 m) then rose to periscope depth, spotted I-168, took aim, fired four torpedoes at 18:12. Zt least one or tow hit from close distance and I-168 went down some 60 nautical miles (110 km; 69 mi) off New Hanover with all hands (97). Presumed lost on 10 September north of Rabaul, she was stricken on 15 October.

I-69/169 (1934)

The Kaidai VIa Early batch I-69 was laid down at Mitsubishi, Kōbe Shipyard on 22 December 1932, launched on 15 February 1934 and completed on 28 September 1935. She was attached to the Kure Naval District at first and on 8 October 1935, assigned to Submarine Division 12, and to Submarine Squadron 2 (2nd Fleet, Combined Fleet) from 15 November. On 13 April 1936, she left Fukuoka with I-68 and I-70 for a training cruise off China (Qingdao area), see above, and back to Sasebo on 22 April 1936, then a trip to Mako, Pescadores in August 1936 and back in September. She was was decommissioned, 3rd Reserve, Kure Naval District from 15 December 1938, atached to the Kure Naval District, 1 May 1939, and recommissioned around 1 September 1939 wit the invasion of Poland. Her unit SubRon 12 was reassigned to SubRon 3, 2nd Fleet on 15 November. She left Okinawa on 27 March 1940 with I-68, I-70, I-73, I-74, and I-75 for a training cruise in Chinese waters (see above). Her unit was reassigned to the 6th Fleet on 15 November. On 12 May 1941 she had a collission and bow damage with I-70 at Yokosuka.

In late 1941 she was assigned to Operation Z, as part of the attack on Pearl Harbor. Her unit joined SubRon 3, 6th Fleet′s Advanced Expeditionary Force and on 11 November she left Saeki, Japan as flagship for the commander of SubRon 12 for Kwajalein and from there departed on the 23th for her first war patrol. After receuving the signal “Climb Mount Niitaka 1208” on 7 December she took up station off the entrance to Pearl Harbor, notably to rescue crews of midget submarines. At 21:01, her commander noted in his log book “massive explosion in Pearl Harbor. Several explosions, followed by high columns of fire (probably detonating warship magazine) sunk by our midget submarines”. On the evening she spotted a passing by destroyer SSE of Barbers Point, Oahu, fired a torpedo but the wake was spotted, and dodged. The DD turned back and followed the wake, and I-69 was depth charged but dived deep.

I-69 and I-68 on 8 December remained close to the entrance of Pearl Harbor, still awaiting the return of midget submarine crews. Aday later, I-69 spotted a cargo ship south of Oahu, launched but missed. The wake was signalled to an escort and she was depth-charged. Later that day, she blundered into an anti-submarine net off Barbers Point. Hours were needed to freed herself but her periscope was bend. She surfaced after being submerged 39 hours. Her mission was abandonedand she withdrew to Kwajalein on 27 December.
Her second patrol started on 12 January from Kwajalein to Midway Atoll for a reconnaissance like her sister (see above). She arrived off Midway on 21 January 1942 and at 18:05 on 8 February 1942, she surfaced 1,000 yards (910 m) off Brooks Channel, ordered to shell by night the radio station on Sand Island. However after just three rounds return fire by a USMC 5-inch (127 mm) coastal battery forced her to submerge. On 10 February she surfaced south of the mouth of Brooks Channel. At 17:58 she resumed the bombardment when two U.S. Marine Corps Brewster F2A-3 Buffal from VMF-221 spotted her and strafed, bombed her. They missed and she dove again after just firing two rounds. She was back to Kwajalein on 17 February.

Her third patrol started on 18 February 1942, she departed Kwajalein for the defense of Rabaul, New Britain, as TF 11 approached for an air raid. After it lost the element of surprise, I-69 was diverted to the east of Wake Island. She was back to Japan on 5 March 1942 for an overhaul at Kure. Her 4th patrol started on 15 April, taking part in thesubmarine patrol line off Wake Island. It was uneventful, and she was back at Kwajalein on 9 May. She became I-169 on 20 May and started 4 days later her 5th patrol in support of Operation MI, the invasion of Midway Atoll, joining a patrol line with I-168, I-171, I-174, and I-175 to intercept reinforcements approaching Midway from Hawaii. The Battle on 4-7 June saw her sister I-168 torpedoing USS Yorktown (CV-5) but herself saw no action and was back at Kwajalein on 20 June.

Her Sixth war patrol started on 9 July from Kwajalein as flagship, SubDiv 12, to make a reconnaissance of New Caledonia, New Hebrides. In July, entered Saint Vincent Bay. On 25 July just 75 nautical miles (139 km; 86 mi) SE of Nouméa, New Caledonia, she spotted and torpedoed her first victim, the Dutch 9,227 GRT cargo ship Tjinegara, by then used as USN troopship from Rockhampton Australia, to Nouméa. It took several torpedo hits to have her sinking for good in the night of 4-5 August. Newt, I-169 made a reconnaissance of Port Vila on Efate, New Hebrides. She was detected and had to flee. She arrived at Truk on 15 August for a refit. She departed 2 days later for Japan, Kure on 24 August, Sasebo on 2 September for an overhaul. She was back to Truk on 18 September and mobilized for the Guadalcanal campaign. On 16 November 6th Fleet commander Vice Admiral Teruhisa Komatsu confered with Admiral Isoroku Yamamoto and decided the submarine would be part of a supply system for the besieged 17th Army on Guadalcanal. I-169 made such trip and returned to Kure n uloading mostly food and ammunition by niht and back to Kure by 3 January 1943.

Early 1943 saw her mobilized for the Aleutian Islands campaign from mid-1942. On 15 January 1943, she left Kure with supplies for the garrison on Kiska and returned to Kure, reassigned to the 5th Fleet for the campaign. She left Kure again on 15 February for Kiska with Japanese soldiers and a Type A midget submarine plus torpedoes to defend Kiska, arriving on 26 February and sischarging men and cargo, then back to Kure on 27 February. She spotted underway a cruiser destroyer on 28 February, was detected and depth-charged. Dge refuelled from the Teiyō Maru on 20-21 March and left Paramushiro a day later for the Bering Sea in the patrol line. She was back at Yokosuka for an overhaul on 9 April 1943. Sghe was reassigned to SubRon 1 with I-2, I-7, I-31, I-34, I-35, I-168 and I-171, 5th Fleet, Northern District. The battle of Attu from 11 May deteriorated and the HQ ordered the submarines to take part in the evacuation of the isolated garrison on Kiska.

On 24 May I-169 left Yokosuka with 1,440 rifles and ammunition plus 2 tons food, joining I-171 and I-175 in a scouting line off Attu to asses the situation before landing. But on 30 May the Japanese garrison was eliminated. I-169 made a reconnaissance of Kuluk Bay, Adak, on 5 June and on the 9th she sailed to Kiska, discharged her cargo and embarked 60 passengers. She left on 10 June, survived by a destroyer whilz surfaced, charging batteries, and arrived safely at Paramushiro, on 14 June. 14–15 June she took cargo from the tender Heian Maru, refueled from Teiyō Maru and departed for another supply run to Kiska. On 17 July 1943 she was ordered to bombard Amchitka Army Airfield at Constantine Harbor, but this was canceled. On 22 July she spotted and reported TG 16.21. She could not attack due to the dense fog. On 28 July the evacuation from Kiska commenced, with the USSMC and army launching Operation Cottage on 15 August. The 28 July the evacuation was already underway and on 10 August I-169 arrived was back at Kure for an overhaul. This was her last Aleutian mission.

After her overhaul she departed Kure on 25 September for Truk, reached on 3 October 1943. She departed Truk on 14 October and joined I-19, I-35, and I-175, vectored on a convoy spotted by I-36 south of Hawaii. On 19 November, I-169 patrolled the Pacific between Hawaii and Marshall Islands when ordered to proceeded to Tarawa (Gilbert) as an US invasion fleet was spotted. On 20 November the landing of Tarawa Atoll and Makin and Battle of Tarawa saw the garrison destroyed by 23 November. On Makin a day later. So on 26 November I-169 was ordered to form a picket line with I-19, I-40, and Ro-38 north of Makin. While surfaced on 1 December she was spotted by a plane but dived and escape. She wa contact with a convoy by sonar but could not pierce the escort screen. She was back to Truk on 9 December. Between December 1943 and January 1944 she was resupplied from Heian Maru, and on 1 January assigned to SubDiv 12 (SubRon 3) with I-171, I-174, I-175 and I-176. On 27 January she sailed for Rabau for a supply mission to Buka and Buin on the 27th. She was back to Truk on 11 March but left on 18 March, returned on 22 March. On 4 April she was anchored in Truk Lagoon, northwest of Dublon, being respplied, her CO and officer resting ashore when at 09:00 the US launched a massive air raid.

The watch officer still on board scrambled the crew to depart and try to submerge. But she was spotted underway by PB4Y-1 Liberator bombers and started diving with deck hatches still open, main induction valve unsecured. She started to flood aft, and could not resurface. Surviving crewmen sealed off the flooded compartments but she was just too heavy, sinking to the bottom in 125 feet (38 m) of water. With the confusion of the air raid,, nobody noticd or reported the loss, and she went missing until a diver dove to investigate, contacted surviving crewmen trappedn by tapping on the hull. An order was given to try rescue the submarine on 5 April with a 30-ton crane and tug Futagami sent there, divors trying to secure a line to the bow but finding I-169 was hard enough for a start. Plus the cable broke. Air hoses through drilled holes in I-169′s ballast were tried but no communication meant the crew was unaware they needed to open air valves to the ballast tanks. Silence fell at 23:00 on 5 April after a new air raid and all men eventually suffocated.

At 22:32 on 17 April USN codebreakers decrypted a message confirming the loss of I-169. Bodies had been reciovered after a new salvage attampt succeeded. There was an enquiry establishing the cover of the engine room was left open and the aft torpedo compartment hatchway was also open. In all the Japanese recovered 32 bodies from her forward compartments and she was renamed “Shinohara” after her CO Lieutenant Shigeo Shinohara ashore when she sank and survived. In May she was finished off with depth charges. But the Allies chose to bypass Truk, she was stricken on 10 June, the wreck rediscovered in February 1972. In August 1973 remains were returned to Japan.

I-70/170 (1934)

I-70 docked in Yokosuka for repairs, 12 May 1941

I-70 was ordered from Sasebo Naval Arsenal, laid down on 25 January 1933, launched on 14 June 1934 in presence of Vice Admiral Yonai Mitsumasa (Minister of the Navy 1937-1939 and PM) and was commissioned 9 November 1935. She was attached to the Kure Naval District, SubDiv 12 as flagship, attached to SubRon 2, 2nd Fleet (Combined Fleet) on 15 November. On 13 April 1936 she departed for a training cruise off China with her sisters I-68 and I-69, Qingdao area, and back to Sasebo on 22 April. They also operated from Mako, off Formosa on 4 August to the Amoy area. By 15 December 1938, she was decommissioned, 3rd reserve, Kure Naval District and from August 1939 was in overhaul at Kure for an improved ballistic torpedo attack computer and the new Type 93 passive sonar with her unit now under SubRon 3, 2nd Fleet from 15 November. Fully recommissioned she left Okinawa on 27 March 1940 for the waters of southern China and stopping at Japanese-held Takao in Formosa on 2 April. Her unit was later reassigned to the 6th Fleet. She was relieved as flagship by I-69 on 26 January 1941 but resumed her role on 30 March. On 12 May she collided with I-69 (gash forward starboard ballast aft as far as her conning tower) and was repaired at Yokosuka.

By 11 November SubRon 3 was reassigned to the 6th Fleet′s Advance Force and was ordered by Vice Admiral Mitsumi Shimizu after a briefing on IJN Katori to be part of the Pearl Harbor attack. I-70 left Saeki Bay, Kyushu on 11 November for Kwajalein and as part of Operation Z she left on 23 November for Hawaii, and was confirmed the attack on 2 December. She was sent to patrol south of Oahu during the attack, trying to ambush any ship would sortie from the port. She remained 25-50 nautical miles (46 and 93 km; 29 and 58 mi) south of Oahu but during the attack she came close to 10 nautical miles off the entrance. Katori tried to contact her but failed. On 9 December 1941 pas midnight she was 4 nautical miles (7.4 km; 4.6 mi) southwest of Diamond Head when she spotted USS Enterprise (CV-6) arriving to enter Pearl Harbor. This was her last probable encounter as the submarine was lost that very day.

At 08:40 on 9 December I-6 spotted USS Enterprise (CV-6) misidentified as a Lexington-class, accompanied with two heavy cruisers, north of Molokai at 20 knots. I-6 attempted but faimed an attack and had to dive. Hours later she transmitted her report, and all submarines in the vicinity including I-70 were sent there in interception. It was assumed the carrier was bound for West Coast. After 06:00 on 10 December, an SBD-2 Dauntless dive bomber from VS-6 patrolled around her carrier and spotted I-70 surfaced, some 121 nautical miles NE of Cape Halawa, eastern end of Molokai. The dive bomber carried a 1,000-pound (450 kg) bomb but missed. The powerful near-miss was enough to jam open at least one hatch, and she could not dive.

I-70 was latter reported by abother VS-6 SBD. She cimbed to 5,000 feet (1,500 m) when I-70 started a slow starboard turn, opened fire hopelessely with her 13.2-mm HMG. Its bomb was another near-miss amidships. This was enough to blow crew members overboard. I-70 after this was observed dead in the water. The SBD remained and saw her starting to sink on an even keel just 45 seconds after this attack. The Dauntless crew saw men jumping in the water through white bubbling and a large oil slinck through the foamy water, and finally debris. She was “presumed lost” with all 93 hands off Hawaii on 15 March and stricken, first Japanese warship sunk in World War II, first IJN fleet submarine lost in this campaign.

I-71/171 (1935)

I-171 departing Kobe on her maiden voyage, 25 December 1941
I-71 was ordered from Kawasaki Kobe Yard, laid down on 15 February 1933, launched on 15 August 1934 and completed on 24 December 1935, then commissioned on 24 December. She was assigned to the Kure Naval District. Her interwar logs are in research. In late 1941 she was assigned to Operation Z on Pearl Harbor in SubDiv 20 , SubRon 3, 6th Fleet′s Advanced Expeditionary Force. On 11 November she elft Saeki for Kwajalein with her Kaidai-6 sisters I-68, I-69, I-70, I-72, and I-73, arrived on 20 November and she departed 3 days later for her first war patrol, when the attack was conformed on 2 December. On 5 December she made a reconnaissance of the Alalakeiki Channel between Maui and Kahoolawe. With I-73 she then roamed the Lahaina Roads between Maui and Lanai, but foundf no traffic.
On 7 December she was sent south of Oahu to intercept ships attempting a sortie. While southeast of Oahu the destroyers swarmed the area soon at the end of the attack and she was detected and depth charged as reported. She surfaced off Johnston Island on 21 December, ordered to bombard the island with her deck gun, until driven off by coastal artillery. She was back to Kwajalein on 28 December.

Her second patrol started on 12 January 1942 from Kwajalein along with I-72 and I-73, relieving I-18, I-22, and I-24 on a picket line off Hawaii. At dawn on 28 January she was in Alenuihaha Channel off Maui, Hana Coast, some 30 nautical miles north of Upolu Point (northernmost point) when she spotted, closed and attacked a three-ship convoy from Kahului to Hilo: The 622t USAT Transport “General Royal T. Frank”, small cargo ship Kalae with a barge in tow, and escorting destroyer minesweeper USS Trever (DMS-16). I-71 fired two torpedoes but missed, but a third struck the transport, which exploded and sank in 30 seconds. 36 men were rescued. She escaped as DMS-16 had no depth charges. She was back to Kwajalein on 16 February.
On 18 February she left Kwajalein for Rabaul, and try to intercept TF 11 approaching for an air raid, however it later cancelled it and withdrew. I-71 was sent instead off Wake Island. She dailed back to Japan at Kure on 6 March and after her unit was disbanded, she ended in SubDiv 12. She departed 15 April for a 3rd war patrol with I-72, uneventful, and she was back to Kwajalein on 10 May. Later she was renamed I-171 on 20 May.

On 24 May 1942, she left Kwajalein for Operation MI and the preliminary phase, Operation K-2: I-121 and I-123 were to refuel two Kawanishi H8K “Emily” flying boats at the French Frigate Shoals, NW Hawaii for a reconnaissance flight over Pearl Harbor, assessing the USN presence here. I-122 was to patrol south of Pearl Harbor to rescue crews of aircraft shot down. I-171 was posted east of the French Frigate Shoals acting as radio beacon for the planes. However I-123 surfaced at French Frigate Shoals by late May 1942 to see a US seaplane base, made of the tenders USS Ballard (AVD-10) and USS Thornton (AVD-11) so this was cancelled. With I-168, I-169, I-174, and I-175 she was sent in a line to intercept reinforcements approaching Midway from Hawaii. She saw no action during the Battle of Midway on 4-7 June and returned to Kwajalein on 20 June.

Her 4th war patrol started on 8 July from Kwajalein for a reconnaissance of Fiji and Samo. The first on 16-24 July, reporting no ships in Suva, and to Samoa, Pago-Pago on 28 July. On 29 July she fored a torpedo but missed an unidentified merchant ship off Tutuila. She sailed for Truk on 12 August, departed after resupplying on 17 August for Japan, Kure on the 24th for an overhaul. The end of the year and early 1943 saw her implicated in the Aleutian Islands campaign. On 15 February 1943, she left Kure with for Kiska. She returned to Paramushiro on 18 March, refuelled from the oiler Teiyō Maru on 20 March and left for her 5th war patrol in the Bering Sea, submarine scouting line. She was back to Yokosuka on 6 April with her unit now assigned to the 5th Fleet′s Northern District Force on 13 May. For her 6th war patrol she headed to reinforce Kiska, attacked underway by a U.S. patrol plane. She was back to Paramushiro on 16 June. On the 26th she left for a 7th war patrol off Amchitka. This was also uneventful and she was back to Paramushiro on 3 August. This was her last northern waters mission.

On 5 August she left Paramushiro for Kure, arrived on 10 August, her unit reassigned to SuRon 3. She left on 17 September for Truk, arrived on the 25th and departed on 7 October as flagship, SubDiv 12 (Captain Hajime Kobayashi) for her 8th patrol, a reconnaissance of the New Hebrides. In between she was radioed by 6th Fleet commander Vice Admiral Takeo Takagi to intercept a convoy of six USN fleet oilers spoted by I-36 south of Hawaii. However the position could nnot be confirmed by the Kawanishi H8K sent from Jaluit. I-171 returned to Truk on 15 November. From December 1943 to early January 1944 she was resupplied by the tender Heian Maru and on 9 January 1944, left Truk for Rabaul, arrived on 13 January, the left again on 17 January for Gali, New Guinea, arriving on 22 January to pick up passengers, and headed for Rabaul, arrived on 26 January. 4 days later she left again for a supply run to the garrison on Buka (rubber supply containers on deck).
On 1 February USS Guest (DD-472) and USS Hudson (DD-475) detected her by night, surfaced, on their radar, just 15 nautical miles west of Buka from 3,500 yards (3,200 m). I-171 spotted them coming, dived, but they regained sonar contact and depth charged her. The attack was devastated and she was signalled “sunk”. Last contact for the Japanese HQ was on 1 February 1944. She was scheduled back on 5 February at Rabaul so by 12 March she was declared “presumed lost”. She was stricken on 30 April 1944.

I-72/172 (1935)

I-72 was ordered from Mitsubishi Kobe Yard, laid down on 16 December 1933, launched on 6 April 1935 and completed on 7 January 1937, commissioned the same day. She was assigned to SubDiv 20, Kure Naval District. On 5 May 1938, she collided with the 60 GRT motor vessel Hachiyo Maru in the Seto Inland Sea, west of Kurahashi-jima (minor damage, but Hachiyo Maru sank). Her interwar whereabouts are unclear. However she was sent in preparation to the Pearl Harbour attack to the Kwajalein Atoll on 20 November 1941. Three days later she left for her first patrol, confirmed on 2 December and arrived off Hawaii on 5 December 1941 for a reconnaissance of Kalohi Channel between Lānaʻi and Molokaʻi, then Lahaina Roads off Maui and radioed the absence of ships there. On the 7th she took position between I-70 and I-73. On 16 December she surfaced off Hilo Bay, shelled Hilo. Three days later she spotted and torpedoed the American 5,113 GRT steamer Prusa, 150 nm south of Oahu underway to Baltimore, by night. She was back on 28 December.
Her second war patrol started on 12 January 1942 with I-71 and I-73 also in Hawaiian waters, relieving I-18, I-22, and I-24 on the picket line, starting patrolling on 21 January and two days later she spotted the 7,383 GRT USN oiler USS Neches (AO-5) underway to join TF 11. Her first torpedo hit was a dud. Her second detonated starboard side aft, and third was on her port side. She surfaced to finish her off with her deck gun when the latter armed with a 5-in/38 answered back, so she dived. Neches later sank by the bow preventing USS Lexington (CV-2) from refueling, cancelling the air strike on Wake Island. She was back on 16 February.
Her third war patrol started on 18 February with I-71, this time to defend Rabaul approached by TF 11 for an air raid but the latter was spotted and was withdrawn, so instead both subs sailed to east of Wake Island. She wazs back in Kure on 5 March for an overhaul. Her unit was disbanded on 20 March so she ended in SubDiv 12, leaving Kure on 15 April for Yokosuka on 3-10 May but back to fix issues and being renamed I-172 on 20 May. On 22 August she left for Truk.
She left on 30 August for the Guadalcanal campaign, and doing a reconnaissance and returnin to Truk on 30 September.
Her 4th war patrol started as flagship of the division, on 12 October to support a Type A midget sub attack on shipping off Lunga Point. On 14 October she was ordered instead to join I-26 south of San Cristóbal to reload batteries of Type A midgets carried by the tender Chiyoda. But this was cancelled again and a day later she was sent to join I-1, I-2, I-3, I-4, I-5, I-7, I-17, I-22, and I-31 or “Group A” southeast of Guadalcanal. After the Battle of the Santa Cruz Group A was dissolved on 28 October and she patrolled southwest of San Cristóbal vs. US supply vessels. This was her last patrol area but historians diverged about her exact fate.

Some says she was sunk by the destroyer minesweeper USS Southard (DMS-10) at the southern end of Indispensable Strait on 10 November, but this conflicts with I-15’s sinking. I-172 was declared missing after 28 October and instead is attributed in Japan to a PBY-5 Catalina “black cat” from VP-11 on 29 October with depth charges. Another spotted the next day a large slick of oil in the same spot. combinedfleet.com however stated I-172 crossed the path of a large convoy on 3 November southwest of San Cristóbal underway for Lunga Point, and reported seven transports. USS Helena (CL-50) detacted her by radar, surfaced, from 16,000 yards (14,600 m) and vectored in USS McCalla (DD-488) at 05:20. She spotted a sub from 2,000 yards (1,830 m) and made a run to ram her. The latter submerged and turned sharply, still showing her periscope off her port bow from just up to 200 yards (180 m).

McCalla began depth charged her at 05:37 and later heard a massive underwater explosion, and a second 30 seconds after, then third and lost sonar contact while crewmen on deck smelled of oil. She was reported sunk. The Dictionary of American Naval Fighting Ships reported instead that I(172 was likely sunk by USS Southard on 10 November 1942 between San Cristobal and Guadalcanal I-172 surfaced. She lost contact after a first attack but regained it hours later and in all maded five more DC runs until spotting oil on the surface and shile investigating it she saw the unknown sub’s bow surfacing 2,000 yards (1,830 m) on the other side of the slick, then dropped 10 degrees and sank by the stern. No confirmation but USS Southard (DMS-10) is credited with her albeit other sources cites I-15. In any case she sank with all hands and was stricken on 15 December.

I-73/173 (1935)

I-73 was laid down at Kawasaki, Kobe on 5 April or 5 November 1934, launched on 20 June 1935, Completed and commissioned the same day on 7 January 1937. She was attached to the Kure Naval District, assigned to SubDiv 20, SubRon 2, 2nd Fleet from 1 December 1937, then SubRon 3, 2nd Fleet on 15 November 1939. She left Okinawa on 27 March 1940 with I-68, I-69, I-70, I-74, and I-75 for training in southern Chinese waters ending at Takao, Formosa on 2 April. On 15 November her unit was reassigned to the 6th Fleet and a day later, she was relieved as flagship I-73. On 11 November 1941 she wa spart of the Advance Force, her skipper briefed on Katori for operation Z. She left Saeki Bay on 11 November with I-8, I-68, I-69, I-70, I-71, and I-72 for Kwajalein and from 23 November left with the division commander aboard for Hawaii, later receiving the signal Niitakayama nobore 1208 on 2 December. She made a reconnaissance of Kealaikahiki Channel between Kahoolawe and Lanai on 5 December, then Lahaina Roads. SubRon 3 on the 7th was deployed south of Oahu, I-73 stationed off the entrance to Pearl Harbor but spotted nothing and departed on 17 December back for Kwajalein via Johnston Atoll that she shelled on 23 December, flattening the Civil Aeronautics Authority homing tower on Sand Islet, but was answered back by a 5-inch gun battery (in all she fired ten rounds, woudning one USMC crew and was back on 29 December.

For her second war patrol as flagship again she sailed with I-71 and I-72 to relieve I-18, I-22, and I-24 on their picket line off Hawaii, reporting her position on 15 January 1942. On 27 January USS Gudgeon was back from her patrol off the Bungo Strait, 240 nm west of Midway when reported by Ultra that I-18, I-22, and I-24 were approaching, she veered in interception but spotted none. Later she detected props off her port bow, rose at persicope depht and spotted I-73 surfaced, running at 5,000 yards (4,600 m) but could not see the number and noted “I-68-class submarine” at 15 knots. She took the aim and fired three Mark 14 from 1,800 yards (1,600 m) but lost sight in heavy seas. Two explosions were later heard the sonar operator noted no propeller noises afterwards and she surfaced to investigate. Her skipper prudently claimed only damage but later Intel confirmed her sank, the first “sub on sub” kill by any US submarine in WW2. other sources credit USS Jarvis, USS Long, on 28 January. Declared presumed lost with all hands on 10 March she was transferred to the 4th reserve, stricken on 15 March.

I-74/174 (1937)

I-74 was ordered on 1934 from Sasebo Naval Arsenal, laid down on 16 October 1934, launched on 28 March 1938 and commissioned on 15 August 1938. She was attached to the Kure Naval District, SubDiv 11, SubRon 2 (2nd Fleet) and on 15 November 1939, transferred to SubRon 3. She left Okinawa on 27 March 1940 with ehr sisters for a training cruise in southern Chinese waters and stop at Takao, Formosa. She wa spresent for the large Imperial review on 11 October at Yokohama Bay. On 15 November she unit was reassigned to the 6th Fleet and her skipped was brirfed on Katori about Operation Z by Vice Admiral Mitsumi Shimizu. She departed on 11 November for Kwajalein, and on 23 November left as flagship of SubDiv 11 for Hawaii, attack confirmed on 2 December and she reached the south of Oahu on 4 December. She remained deployed south of Oahu but herself was on lifeguard duty south of Niihau, departing on 17 December for Kingman Reef, northern Line Islands, 23-25 December and back to Kwajalein on the 31st.
Her second patrol started with her sister of SubDiv 11, I-75, on 13 January 1942 for Midway Atoll, Northwestern Hawaiian Islands, on order to reach the Aleutian Islands. From there she returned to Yokosuka on 19 February. She departed on 15 April to form a patrol line east of Japan. She never saw the sixteen B-25 Mitchell bombers flying towards Japan. They came from USS Hornet (CV-8) for the Doolittle raid to strike targets on Honshu on 18 April. The air group in cover from USS Enterprise (CV-6) attacked the picket line and I-74 later rescued men from the guard boat Iwate Maru No. 1 sank the same day, later transferred to Kiso on 23 April. She was back at Kwajalein on 10 May.

On 20 May as I-174 she was mobilized for Operation MI, and for them, Operation K-2: I-121 and I-123 would refuel two Kawanishi H8K at French Frigate Shoals while I-174 would patrol south of Pearl Harbor to rescue crews but on site were found the tenders USS Ballard (AVD-10) and USS Thornton (AVD-11) so this was cancelled. I-174 and I-175 supported the invasion of Midway until 7 June but none made contact and were back at Kwajalein on 20 June. She left for a 3rd patrol on 9 July to Port Moresby, New Guinea, however an oil leak developed, forcing her back to Rabaul for repairs on 23 July.
She departed a day later, and was ordered instead to take a patrol line off the east coast of Australia and Sydney, then the Nouméa (New Caledonia) area. Next she was sent to the Solomons in August and was back to Rabaul on 17 August. Her 5th patrol with her sister and I-11 was southwest of Rennell Island, southeast of San Cristobal (Solomon Islands) until back to Truk on 22 September. After a refit she departed on 16 October for her 6th war patrol south of Rennell Island in “B Group”, her, I-175, I-9, I-15, I-21, and I-24 and back to Truk on 4 November. She departed on 6 November for Kure and an overhaul, starting on the 12th. Her unit was disbanded on 15 March 1943 and she joined SubDiv 12, SubRon 3, departing on 5 May for Truk.

For her 7th patrol she was ordered off the east coast of Australia and off Sandy Cape, Fraser Island, Queensland, on 27 May. At 03:20 on 28 May she was spotted by a Bristol Beaufort from RAAF’s No. 32 Sqn by radar from 4.5 nm (8.3 km; 5.2 mi) by night when surfaced to reload batteries. Ready to attack, the Beaufort spotted her at 600 yards (550 m), but she crash-dived. Next she surfaced 70 nm (130 km; 81 mi) east of Brisbane on 1st June when spotting a 6,000 GRT which was in reality the US 3,300 GRT cargo ship “Point San Pedro” from Balboa, Panama. She fired four torpedoes at 11:36, but missed, the cargo crew reporting two trailed passing in front of her bow. Next an Avro Anson of RAAF’s No. 71 Sqn left Queensland in search for I-174 and on 2 June six Ansons from Lowood and Coffs Harbour in New South Wales also looked for her bu she was never discovered and resumed her patrol. While off Brisbane on 3 June she spotted an Allied convoy of six transports, three destroyers from 16,250 yards (14,860 m), surfaced at 18:00 in chase but corvettes showed up at her tail and she had to dive as the rear of the convoy turned toward her. Later she was submerged off Cape Moreton, South East Queensland at 08:45 on 4 June when spotting the 4,113 GRT USAT Edward Chambers from Balboa, but she was unable to close and instead surfaced to give chase and started firing her deck gun, firing 9 rounds and missed, but summerged as she was fired in return. Later an RAAF Beaufort of No. 32 Sqn was sent to search for her and later HMAS Bendigo escorting Convoy PG53 just 11 nautical miles (20 km; 13 mi) northeast of the cargo was detached, then five more Ansons. Meanwhile I-174 headed south.

At 10:25 on 5 June while 60 nm northeast of Coffs Harbour she made sonar contact with Convoy PG53 from 13,000 yards (11,900 m) and in bad weather and poor visibility, she surfaced to give chase at 12:55, closed to 1,600 yards (1,500 m) behind until flew over by Allied patrol aircraft so she submerged and later resumed the chase. At 20:22, she was 5,000 yards (4,600 m) to the convoy’s starboard, and was about to setup an attack at 4,000 yards (3,700 m) when spotting an incoming destroyer ahead of the convoy. She resurfaced at 21:45 but the same happened. She then started a high-speed run ahead of the convoy, submerged to await approach, but when she surfaced at dawn on 6 June the convoy had changed course and she was 21,500 yards (19,700 m) at its port quarter. The pursuit was dropped and instead the proceeded off Newcastle, New South Wales. While 100 nm (190 km; 120 mi) east of Sydney on 7 June she spotted the 7,176 GRT Liberty ship SS John Bartram from San Francisco, zigzagging. She closed the range and placed herself ahead, fired four torpedoes with two spotted by lookouts. I-174’s crew heard two explosion, then a 3rd, mistook for a depth charge explosion so she dove deep. The ship was reported sunk but she survived. Al three “hits” were duds or safety explosions. Next she headed east and spotted a ship but was depth charged. On the evening of 9 June she was in the Tasman Sea, found no ships until 13 June but spotted later an Allied convoy 30 nm east of Wollongong Light, too distant for attack. So she started to head north, spotted an Allied warship in the evening when surfacing, and dived. Later a Bristol Beaufort gained contact on her at 22:50 on 14 June, bombed I-174 but missed. She crash-dived, remained submerged for 35 minutes, was attacked again when she resurfaced, this time with a near-misse off her port side, crash-dived again, resurfaced and the Beaufort was out.

At 01:00 on 16 June she was off Smoky Cape, New South Wales, SE Coffs Harbour when at 16:37 she spotted Convoy GP55 (10 caro, 3 LST, corvettes HMAS Kalgoorlie, HMAS Warrnambool, HMAS Deloraine, HMAS Bundaberg, and HMAS Cootamundra). She fired two torpedoes at transports, one struck USS LST-469 starboard, killing 26, wrecking her steering gear. lookouts on the 5,551 GRT USAT Portmar spotted the second approachin and her skipper ordered a hard turn to port, but she was hit on the starboard No. 1 hold and her gasoline cargo exploded, her crew jumped out as her ammunition exploded shortly afterward. She was the last ship sunk by a Japanese submarine off Australia′s east coast. LST-469 was towed to Sydney for repairs. Kalgoorlie and Warrnambool attacked I-174 but she escaped.
On 20 June I-174 was ordered to return to Truk via the Solomons, arrived on 1 July 1943. She left on 9 August for Rabaul making a first supply run from 31 August to Lae, New Guinea, on 2 September and back 2 days later. She carried Rear Admiral Kunio Mori as passenge whend epartinf on 7 September for Lae (9th) and pick up the relieved Rear Admiral Ruitaro Fujita, Army staff officers and 30 sick IJA soldiers, bound for Rabaul. She was attacked a day after on 10 September and eventually surfaced and proceeded later to Rabaul, but was bombed and missed by B-17 Flying Fortress on 12 September just before calling port. Her squadron was disbanded on 15 September and she was atatched directly to 6th Fleet HQ. She started another supply run on 19 September for Finschhafen (21st) and back. Meanwhile Finschhafen was invaded (Huon Peninsula campaign) so she was ordered to attack TF 76 supporting the landing, but missed them and returned to Rabaul on 24 September.
Her last New Guinea supply run started on 29 September , to Sio, arriving on 1 October, unloading cargo and back to Rabaul on 11 October, then Truk on 16 October.

As part of the Gilbert/Marshall campaign; landings on Tarawa, Butaritari and Battle of Makin 6th Fleet’s Vice Admiral Takeo Takagi ordered I-174, I-175, I-19, I-21, I-35, I-39, I-40, I-169, and Ro-38 to attack the landing force. I-174 left Truk on 24 November for her 8th patrol to join a line northwest of Butaritari. On 1 December an aircraft reported a convoy heading toward Butaritari, with the closest, I-21 and I-174 sent to intercept. I-21 was probably sunk on 29 November, I-174 missed the convoy. By nifght on 6 December, I-174 was reloading batteries some 30 nm east of Tarawa when her lookouts spotted a destroyer so she She crash-dived, was depth-charged, with her diesel engine compartment and electric motor compartment flooded. As her battery and oxygen ran out, she was forced to surface and fight it out, but managed to escape into a rain squall and returned to Truk on 10 December. She left on 23 December for Kure, arrived on 30 December for full repairs until 3 April 1944 and sent for her 9th war patrol from Truk to the Marshall Islands. Her last report was from the south of Truk on 10 April 1944 and she never was heard of again. It is agreed today that she was sunk on 12 April 1944 by a PB4Y-1 Liberator from VB-108 with bombs as she submerged southeast of Truk. Later an oil slick and floating debris were spotted and this matched postwar examination. She was declared presumed lost 13 April, stricken on 10 June.

I-75/175 (1936)

I-75 was ordered in 1934 from Mitsubishi Heavy Industries in Kobe, laid down on 1 November 1934, launched on 16 September 1937 and commissioned on 8 December 1938, attached to the Kure Naval District and SubDiv 11/Subron 2/ 2nd Fleet. On 15 November 1939 this was SubRon 3/ 2nd Fleet. She left Okinawa on 27 March 1940 with I-68, I-69, I-70, I-73, I-74 for a training cruise in southern Chinese waters ending at Takao and took part in the 11 October Yokohama Bay Imperial fleet review. On 15 November her units was reassigned to the 6th Fleet and on 11 November 1941, was briefed on Katori for Operation Z, she was assigned to the Submarine Advance Force on 11 November and left Saeki Bay with I-74 for Kwajalein, arrived the 20th, sailed for Hawaii and deployed on the 7th south of Oahu. Later she shelled the harbor at Kahului, north coast of Maui on 15 December (16 rounds), damaging the Maui Pineapple Co. On 17 December she torpedoed and hit the 3,545 GRT merchant ship Manini south of Hawaii, surfaced and illuminated her with the searchlight ready to gun her down, to see her sinking by the stern. USS Patterson (DD-392) later rescued her lifeboat’s survivors on the 28th. On 24 December while back she shelled NAS Palmyra, northern Line Islands (12 rounds) on the radio station, and USMC dredge Sacramento anchored in the lagoon. But coastal artillery forced her to submerge and she was back at Kwajalein on 31 December.

The sisters left on 13 January 1942 for Midway and the Northwestern Hawaiian Islands, then the Aleutian Islands and Yokosuka on 19 February. She departed on 15 April and was at sea on a patrol line when the Doolittle Raid happened on the 18th. She arrived at Kwajalein on 10 May and on 20 May as I-175 she left Kwajalein for Operation MI/Operation K-2, the takeover of French Frigate Shoals, whuxh was later cancelled as they were preceded by the USN. They took no direct part in the Battle of Midway and returned to Kwajalein on 20 June. She left on 8 July for the Tasman Sea and eastern coast of Australia for patrol, starting on 20 July. While off Newcastle, New South Wales on 23 July she spotted and attacked, declared “sank” the 3,279 GRT merchant ship Allara (single torpedo). But the ship was evacuated, survived, was reboarded later and brough to port for repairs. On 24 July she also assumed sunk but damaged the 3,345 GRT Murada off Crowdy Head northeast of Newcastle. On 26 July she was depth-charged by HMAS Cairns. She then torpedoed and sank the French 2,795 GRT Cagou carrying nickel ore from New Caledonia 160 nm northeast of Newcastle on 28 July.

On 3 August she was surfaced when spotting the 233 GRT trawler Dureenbee off Moruya, fired her main gun but missed, and the latter reported her position. She lighter her up with her Heavy machine guns, destroying her radio room followed by two 120 mm shells destroying the wheel house, steam engine. I-175 circled her, firing for 45 minutes, but dove as she refused to sink. The ship wa slater located by a RAAF aicraft and the men rescued. Later the trawler Mirrabooka founf her aground on 4 August on New South Wales, North Head of Batemans Bay. Claimed postwar as a war crime, it happened that some were used as pickers and US subs did the same to cripple Japan’s war economy. On 5 August she was off Jervis Bay. 2 days later she was recalled to take part in the Guadalcanal campaign, sailed west of San Cristobal, southeastern Solomons via New Caledonia. On 12 August while 170 nm southwest of Espiritu Santo she was spotted by two SBD-3 Dauntless from USS Saratoga (CV-3) and attacked. She submerged but the heavy bom near misses caused damage. Later she was hunted down by USS Grayson (DD-435) and USS Sterett (DD-407) detached from Saratoga′s escort screen but she escaped and returned to Rabaul for emergency repairs from 17 August. She made a new patrol from 22 August southeast of Guadalcanal, Rennell Island and San Cristobal to reconnoiter the anchorage at Lungga Roads on 11 September. She was back at Truk on 21 September.

Her 6th patrol started on 16 October in a patrol line with I-174 southeast of the Indispensable Reefs and Shortland Islands.Later they joined I-172 and Ro-34 to intercept a convoy but missed. She was back to Truk on 19 November. Later assignd to the B Patrol Unit (I-174, I-9, I-15, I-21, and I-24) she was rammed and damaged on 20 November in Truk Lagoon south of Eten Island by the 16,764 GRT oiler Nisshin Maru, run aground to prevent sinking. Patched up, she departed Truk on 27 November for Kure (4 December) the Yokosuka (5th) for full repairs, her unit disbanded on 15 March 1943, she joined SubDiv 12, SubRon 3. After repairs and overhaul she departed Kure on 17 May 1943 for the Aleutians. On 21 May she was tasked of an evacuation of Kiska, but 3 days later, sent instead 200 nmi south of Kiska for a planned counter-landing on Attu. But the Battle of Attu was a failure and she was sent to Paramushiro, northern Kurile and on 5 June departed for a supply run to Kiska and back to Paramushiro on 10 June. Refuelled by Teiyō Maru on 11 Juneshe left 2 days later to Kiska, landed stuff on the 17th back on the 20th. She left on 24 June for an 8th war patrol against US shipping south of Amchitka with I-171 but made no contact and was sent to Kure on 10 August as Kiska was evacuated.

For her 9th war patrol she left Kure on 19 September for Truk on the 25th and departed on 16 October for Wake Island. On 20 October I-36 reported a large convoy south of Hawaii heading west, so she was along I-19, I-35, and I-169 sent there but failed to make contact. She was back to Truk on 20 November. She was ordered to Butaritari at flank speed and arrived on 24 November and located, approached a task force 20 nmi (37 km; 23 mi) off Butaritari. She detected USS New Mexico (BB-40) at dawn, submerged, approach, and at 05:10 fired four torpedoes: 2 missed USS Coral Sea (CVE-57), but one hit USS Liscome Bay, preparing to launch aircraft at 15 kts. She was struck on her starboard aft of her after engine room and this lucky hit trigerred her bomb storage magazine. Her stern disintegrated. Debris fell on all ships around, inluding the nearby USS New Mexico but USS Kimberly (DD-521) gained sound contact and attacked. Liscome Bay sank notably with the the commander of CarDiv 24 and TG 52, Rear Admiral Henry M. Mullinnix as well as Captain Irving D. Wiltsie and 591 enlisted men plus officers. Navy Cross recipient Cook Third Class Doris Miller (a Ford class aircraft carrier named after him is schedule) was among thiese. 23 aircraft also went down but five remaining aloft were picked up by USS Lexington and USS Yorktown (CV-10). 272 men were rescued. This was the greatets success of any submarine in class, pas USS Yorktown for the lead boat.

On 26 November I-175 reported the attack, and her damage after 6 near miss of depht charges. The aircraft carrier was noted “probably sunk”. On 27 November her engineers consluded she could hardly control her diving depth so she went back to Kwajalein on 27–28 November to refuel, proceeded to Truk, reached on 1 December 1943 and CO Nao Tobata received a personal citation on 8 January 1944 from Vice Admiral Takeo Takagi. She left Truk on 27 January as flagship SubDiv 12, for her 10th war patrol northeast of the Marshall Islands. In between there was landing at Kwajalein and Roi-Namur so with Ro-39 she was ordered to Wotje Atoll, Marshalls, at flank speed and arrived on 3 February. She was located by radar by USS New Jersey (BB-62) east of Wotje at 22:03 on 3 February, just 21 nmi (39 km; 24 mi) away so USS Charrette (DD-581) was detached to investigate and gained contact, but lost it at 10,300 yards (9,400 m), which indicated a submerging submarine so she regained sonar contact and on 4 February just past midnight starter her attack, before losing contact. USS Fair (DE-35) arrived 35 min later and fired a salvo of 10 Hedgehog charges. Charrette and Fair recorded four explosions. I-175 was killed by these, some 100 nmi (190 km; 120 mi) northwest of Jaluit Atoll. USS Nicholas (DD-449) is sometimes credited for her on 17 February northwest of the Marshalls. She was declared presumed lost on 26 March, struck on 10 July.