The fleet's spearhead

In December 1941, the most valuable asset of the Imperial Japanese Navy, after the aircraft carriers of the combined 1st air force (Kido Butai), were its Cruisers. Indeed, contrary to the older, slower battleships, cruisers were built along along the interwar and perfected until stopped during the war itself, when fewer resources were available.

All in all, despite having formidable offensive assets, IJN cruisers performed actions in dispersed order depending of their age and capabilities. The real spearheading ones were only twelve: The four Myoko, the four Takao and the four Mogami. They were the most recent, best armed, largest of the IJN and indeed took part in the most offensive fleet units of WW2 in the Pacific.

The older 1920s vessels of the Tenryū, Kuma, Nagara and Sendai classes were stil transitional WWI designs which were arguably obsolete in 1941 and were sent to aid eny convoy which needed protection; thus logically sidelined and never used in first line units. The experimental Yubari followed that path, but the more potent Furutaka and Aoba classes at least saw more frontline action. Wartime vessels such as the Tone were in effect the last "heavies", joining the pack, but the four Katori were essentially schoolship with little military value, and the four Agano were rather more escorts than frontline cruisers.

Special mention to the never-built B-64 though. These "large cruisers" to keep the US denomination adopted for their Alaska class, proven to be an imaginary threat were indeed planned by the IJN high command planning the end of peactime limitation, as a "cruiser hunter".

Legacy: WW1 cruisers still in service

Postwar cruiser development: Yuzuru Hiraga's design school

The 1933 Tomozuru incident and consequences

Characteristics of IJN Cruisers

A three phases evolution

Armament

Powerplants and performances

Protection

IJN Cruisers in action in WW2

Tactical Principles

Reality of combat in WW2

IJN's Agano class were still a prewar project completed in wartime, IJN Oyodo being the real only Japanese wartime cruiser (launched 1943). To compare at the same time, the USN laid down more than 65 keels for light cruisers (Cleveland and Atlanta class) and 30 keels for heavy cruisers, completing most of them, the Royal Navy itself commissioning also many new cruisers during that time.

This lack of resources meant efforts were concentrated on aircraft carriers, escorts, "secrets weapons" such as the Kaiten submarines, or Shinyo Motor Boats, the Yamato and Mushashi absorbing most of available the resources in 1941-42. Would more cruisers had changed the nature of the fight in 1942-43 ? Not really, as air power was the dominant factor, but until the Japanese retired from Guadalcanal, operations were mostly led by Cruisers, especially by night, and they proved very efficient.

Nomenclature of IJN cruisers

IJN Nagara

IJN Isuzu

Isuzu rebuilt in 1944

IJN Isuzu was built at the Uraga Dock Company. She was commissioned on 15 August 1923 and participated in the second war with China, covering landings in China, and the capture of Hong Kong. Reassigned to the Dutch East Indies, for the landings and battle of Java, she also later took part later in the Solomon Islands campaign. She was present at the Battle of Santa Cruz and the Naval Battle of Guadalcanal. Almost sunk due to air attacks in late 1943, she headed back to Japan to be rebuilt into an anti-aircraft and anti-submarine cruiser. She participated in the Battle of Leyte Gulf, sunk later by a "wolfpack" of three US submarines and one British, off Sumbawa, 7 April 1945.

IJN Natori

IJN_Natori_in_1922_off_Nagasaki

IJN Natori was built by the Mitsubishi Naval Yard in Nagasaki, commissioned on 15 September 1922. In 1937 and afterwards, she covered troops landings in China and in early 1942, took part in the Phillippines invasion. She also took part in the Dutch East Indies campaigh, notably contributing during the Battle of Sunda Strait, to torpedo the cruisers USS Houston and HMAS Perth. Next she stayed patrolling in the Dutch East Indies waters before a refit and repairs in Japan after air attack in June 1943. She was back in service by April 1944, sunk off Samar by USS Hardhead, on 19 August 1944.

IJN Yura

IJN Yura was commissioned at Sasebo Naval Arsenal, on 20 March 1923. She was pat of the fleet shadowing Force Z (Prince of Wales and Repulse) in december 1941. Later in January 1942 she covered the landings of Japanese troops in Malaya and Sarawak. She also took part in the Indian Ocean raid, and was part of Nagumo's escort at the Battle of Midway. She also later took part in the Battle of the Eastern Solomons. Badly damaged after a sever air atack in the Solomons, she was scuttled to prevent capture on 25 October 1942.

IJN Kinu

Japanese_cruiser_Kinu_in_1931

IJN Kinu was completed at Kawasaki Shipbuilding Corp., Kobe, on 10 November 1922. She was part of the fiorce shadowing Prince of Wales and Repulse and like her sister Yura also took part in the landings of Japanese troops in Malaya and the Dutch East Indies. She took part in many combat missions in the Solomon Islands and the Philippines. She was ultimately sunk by USN aviation in the Visayan Sea, on 26 October 1944.

IJN Abukuma

Abukuma_cl1941

Last of the Nagara class, IJN Abukuma came from the Uraga Dock. She was commissioned on 26 May 1925, part of the escort force assigned to the kido Butai at Pearl Harbor. She was later also the sole Nagara class ship at the Battle of the Komandorski Islands (north pacific), remaining active in northern waters until October 1944. She was rushed south to oppose the American invasion of the Philippines, caught and attacked, severely damaged by ambushing American PT boats, at the Battle of Surigao Strait (25 October) finished off by land-based bombers and eventually scuttled on 26 October 1944.



The two heavy cruisers of the Furutaka class were the first built by the Japanese Navy after the Washington Treaty. Their main feature was the presence of a continuous deck with two successive recesses, a measure to save weight to optimize speed, but also the choice of an artillery in six simple turrets.

This singular configuration did not proved advantageous and the two ships were rebuilt in 1936-39. Significant changes included the more rational choice of double turrets, reconstructed superstructures and bridge, and lateral torpedo tubes. 12 tubes, 6 twin banks two on each side replaced by two quadruple banks.

A catapult was also fitted, as well as the installation of anti-torpedo ballasts, the reinforcement of the overall protection and the AAA, with a tonnage passing from 7,100-8,450 tons to 8,700-10,340 tons. Originally, this AA artillery consisted of only four 100 mm pieces and two heavy machine guns. In 1932 these were replaced by QF 120 mm fully shielded in half turrets, while 25 mm guns and other heavy 12.7mm machine guns were added to this range.

By the new standard they imposed, the Furutaka led to the Aoba, barely larger, but improved. They participated very actively in the Japanese operations, particularly in the Solomon Islands, and were both sunk, the Furutaka off the island of Savo, Guadalcanal, during the battle of Cape Hope the night of October 11 to 12, 1942, being part of the “Tokyo Night Express”, by the American cruisers of Admiral Scott. The Kako was torpedoed and sunk near Kiaveng (New Britain) by the old American submarine S44, August 10, 1942. She participated shortly before the great victory at Savo Island.

Specifications
Displacement 8 700 t. standard -10 340 t. FL
Dimensions 183,53 x 19,93 x 5,61m
Propulsion 4 shafts turbines, 12 boilers, 102,000 hp, 33 knots
Armor: 25 to 76 mm
Armament: 6x 152 (3×2), 4x 120, 8x 25 AA, 4x 13.2 mm HMG AA, 8x 610 mm TTs (2×4), 2 seaplanes
Crew: 730

The Nachi: First true IJN heavy cruisers

The heavy cruisers of the Nachi class laid down between 1924 and 1925 and completed in 1928-29, were at the very limits of the Washington Treaty, yet they managed to bear a five turret arrangement never seen on a ship of this type before, and imposing to the IJN new standard, not followed internationally but coherent with Japanese retirement of the league of nations.

This feat consisted of being able to stack five twin turrets for 8-in/203 mm guns and 12 torpedo tubes on a cruiser more than 200 meters long, but which ultimately displaced only the 10,000 tons required by the treaty. They could reach 35.5 knots without excessive power either. The secret laid partly in their amazing width/lenght ratio almost unchanged from the Aoba, about the same 12/1. Their protection was greatly improved however with an inner armoured citadel and a triple hull plus reinforced coss-sections and a reduced but reinforced bulkhead. In fact, the final tonnage as for 1941 was 11,000 tons.

IJN Ashigara an the Gref Spee in the background at Kiel in March 1937. Colorized photo by Hirootoko JR.

1930s et 1940s refit

In 1934-36, their single 120 mm single mounts gave way to new 127 mm (5 in) twin turrets, their fixed torpedo tubes replaced by quadruple rotating banks, while the AA was reinforced by four additional 13.2 mm machine guns and two catapults were installed on the sides to launch reconnaissance floatplanes. In 1940-41 there was a second overhaul concerning the masts and superstructures, the addition of 8 x 25 mm AA guns and especially two new quadruple torpedo tubes on the flanks, for a total of 16, a record for a cruiser, but in the typical trend of aggressiveness of the Japanese tactics at the time. This forced to add imposing bulges in order to safeguard their stability.

IJN Nachi in Yokosuka in the 1920s. Colorized photo by Hirootoko JR.

Specifications

Displacement 13,000 t. standard -14,740 t. Full Load Dimensions 203.76 m long, 20.60 m wide, 5.66 m draft Propulsion 4 propellers, 4 turbines, 12 boilers, 130,000 hp. Top speed 34 knots Armour from 100 to 25 mm Armament 10 guns of 152 (5 × 2), 8 guns of 12, 8 of 25 AA, 12 mitt. 13.2 mm AA, 16 TLT 610 mm (4 × 4), 3 aircraft Crew 773

The Nachi class in action

In operations, these four ships, the IJN Nachi, Myoko, Ashigara and Haguro proved formidable combatants, very actively employed, and which defeated all their American, British and Dutch opponents until 1943. The Myoko was apparently the only one to have been camouflaged. These Nachi class cruisers participated in the battle of Leyte, where the Nachi, in the confusion and fury of the attacks, collided and seriously damaged the Mogami.

Shortly before this battle, their AA armament had reached fifty-two 25mm guns, at the cost of removing two banks of torpedo tubes. They survived the battle of Samar (Leyte), the Nachi being sunk in November 1944 off Manila by USN air attacks, while IJN Myoko, already badly damaged in Leyte, was torpedoed by USS Bergall in December 1944 but survived.

She sank in shallow waters in the Strait of Malacca, and her wreck was dynamited in 1946 to allow trade to resume. IJN Haguro and Ashigara were sunk respectively in May and June 1945, one by the torpedoes of British destroyers off Penang during the reconquest of Malaysia, while the second was torpedoed by British submarine HMS Trenchant in the Bangka Strait.

Myoko 1944 - author's schematics

Cruiser Myoko on sea trials in March 1941 in Sukumo Bay. Colorized photo by Hirootoko JR.