UC-I class U-Boat (1915)

Coastal Minelaying Submarines – 15 completed 1915: UC-1 to UC-15

The Type UC I coastal submarines were small minelaying models built in 1914-15, the first type of three that were part of the German all-out U-boat war. They were not the first operational minelaying submarines in the world, but the first class, with fifteen boats built and joined the Flanders flotilla. Four also went to the Pola Flotilla, Adriatic. They were coastal modes, just 168 tonnes, with a single shaft, and had their issues, and only carried 12 mines. But comparatively to their size they sank collectively far more shipping that expected, 264 ships for 283,000 GRT. UC-6 alone sank 64.064 GRT, so 380 times her own tonnage. Needless to say, this was a stunning success, and the Kaiserliches Marine immediately prepared a second improved design, the UC-II.

UC-5 under British hands, deady to depart for her first exhibit. Note the mine on a pedestal.

Development

Russian Krab: The idea.

The development of coastal submarines started in 1914 with the intent to be able to deploy these by rail in knock-down kits anywhere the German Imperial Army could take ports. This was the case of the Flanders. Two types of “Küsten U-Boote” were developed, the UB-I, standard coastal submarines, and the UC-I alongside, a bit larger to carry mines instead. They were pure minelaying models, having no torpedo tubes. The idea of a minelaying submarine was not invented by Germany, but a Russian concept: The Krab. Krab in short had been a concept invented by engineer Naletov in the Russo-Japanese war back in 1904 when seeing the efficience of mines. His first two models were too small to really be efficient as they were privately funded, but with the right connection in the admiralty he managed to get a more consistent design accepted.

Krab, a parallel Russian development and possible inspiration.

The Krab was reworked by other engineers and eventually the design prepared in 1907 by the Nikolaev Naval shipyard. Approved only by 1909, construction dragged on, until launched in 1912 and completion in 1915 so by that stage, even it was the first of its kind and by far the most ambitious, Krab ended not as the first as the Germans just went faster. The Germans indeed worked out their own program on 18 August 1914, ten days after the start of World War I. It was rejected at first, then relaunched after the success of the UB-I in November, leading to the UC-I ordered from Vulcan, Hamburg, built at a record pace in 5-6 months, with the first boats operational by 7 May 1915, two months before Krab (in July). But they were quite small and limited, when Krab could launch 60 mines from dedicated caterpillar style longitudinal tunnels. But Krab was a rather large (500/700t) boat with a ram bow, when the German UC-I type was a completely different animal. What is unclear is how much the Germans knew about her. In 1912 her launch was a public ceremony, nothing secret about it.

The conversion from the small, practical UB-I that could be carried by rail anywhere, to the same type of U-Boat but modified to lay mines, was a no brainer for the “U-boote” faction in the Kaiserliches Marine. They were near invisible and it was less risky to have them sent forward than surfaced minelayers like the converted Königin Luise attempting to mine the Thames estuary and sunk the first day of the war. The UC-Is could do the same on paper, but the idea was not accepted outright. On 11 September the project was indeed rejected by Von Tirpitz. However on the 25th, as the German Army advanced in Belgium and reached the coast, it was revived. In between also, the spectacular sinking of HMS Aboukir, Hogue, and Cressy all by U-9 Admiral Tirpitz to completely revise his long-held optinion against U-Boats and agree to initiate the construction of new types.

Design 35a

Base plan and cutout, reconstructed, courtesy of https://virtualdockyard.co.uk

The Naval Ministry approved the Design 35a on October 9, 1914—despite a negative assessment from the newly established U-boat Inspectorate. Naval yards were contacted also to design a rail-transportable coastal U-Boot and by 15 October 1914, Germaniawerft came out with essentially a modified UB-I type design. Indeed the same day, fifteen Type UB I were just ordered. Their modular construction made to ease transport also facilitated a much shorter construction time of just four months. Taking the UB I as base, the Kaiserliches Marine could expect the new UC-I types to be ready in the same short span.
The Torpedo Inspectorate worked the design under the direction of Dr. Werner and it was later designated as the UC I class for production.

Thus the UC-I was eventually ordered on 23 November, a month and a week later, fifteen Type UC I U-boats. But both Kaiserliche Werft Danzig and Germaniawerft could not take on the orders, their hands were already full. So instead AG Weser was contracted, having just started with the Type UB I. Five Type UC I were thus ordered there, alongside ten from AG Vulcan yard in Hamburg, both promising between five to six months in construction.
Indeed in total, a series of 15 Design 35a types were ordered on November 23, as part of the wartime fleet expansion program with the first ten (UC-1 through UC-10) awarded to Vulcan and five (UC-11 through UC-15) from AG Weser, Bremen and they were indeed launched and commissioned between April and July 1915 making them the world’s first minelaying submarines. Sure, they were infintely less capable than Krab, but the later took more than a decade to go from concept to commission. The Germans just chose the more pragmatic, fast approach from project to commission, in less than a year.

Design of the class

Hull and general design

Postwar reconstruction of the UC-I type plans with all cutaway references, courtesy of https://virtualdockyard.co.uk

The UC I-class were based on the UB-I, and so were still quite small, purey coastal, and single-hull submarines (without blisters but internal ballasts) and an overall length of 33.99 meters (111 ft 6 in), a beam of 3.15 meters (10 ft 4 in), and draft of 3.04 meters (9 ft 11.7 in). They displaced 168 tonnes (165 long tons) surfaced and 182 tonnes (179 long tons) submerged. The Bremen boats however were a bit different: UC-11 to UC-15 indeed displaced 183 tonnes (180 long tons) submerged for a draught of 3.06 m (10 ft 0.5 in). Their height, from the keel to the top of the conning tower was 6.3 meters (20 ft 6 in).
Now for the general outlook, the hull featured the same rounded bow and cylindrical conning tower as the UB-I (1.3 m (4 ft 2 in) in diameter) enclosed in a streamlined fairing with an access to the interior was provided by two hatches, one in the conning tower and another in the aft section leading to the crew quarters.

The hull lines were not as edgy as later U-Boat to maximize speed however, they were “trucks” with the bow widening quickly (in less than 2 meters) to its max beam at the height of the forward diving planes, to house the mine wells section. There were six of them, not vertical but slanted in order for a slower, more controllable drop. Each hold two mines completed with their heavy lead foot sinker and mooring cable with initial electric setup from inside the boat. On both sides are located the four froward main ballast tanks and trim tables. In addition they had a 136 kg mushroom anchor.

There were more ballasts furyer aft on both sides of the forward and aft battery holds. The latter were located under the main deck inside the hull which was basically both the outher and pressure hull wo with thick plating. The tube for the conning tower was shaped as a cyinlinder, in which went the hatch, and single Zeiss periscope (watch model) and the tube for the telescopic antenna to be deployed when surfaced and cabled out on both ends for short ranged wireless radio communication.

Given the large space taken by the mine wells, about 2/5 of the entire hull crew quarters started short of the conning tower and control room, wnd they were quite cramped. The presence of the mine tubes forward preclused the installation of any torpedo tubes and the entire aft space was taken by the single diesel unit and electric motor (see below) for its single shaft. The cross-style tail aft comprising a cut through “M” shaped rudder had enough space for an internal aft plane to move up and down, but to some degree. The tail unit was protected on its side by crescent shaped bars and below by a large belly fin also protecting the single shaft. For more internal data just chekout the plan.
The UC-I had a crew of 14 men, with shareable “hot bunks” due to the lack of space through quarters. A Lieutenant Zür See commanded the boat, without XO but a quartermaster. All NCO/sailors had doubled or triple tasks to work in quarters and replace each others at each post.

The UC-I were not very popular through. The large battery wells below the deck make the whole internals too cramped to fully stand. Plus the boats were virtually unarmed apart their mines, an indirect weapon. There were a few small arms (pistols and perhaps a single K98 short variant rifle) in a locker and a 8-millimetre (0.31 in) machine gun on deck for defense. This lack of defense and potential lost opportunities led to the experimental installation on UC-11 in 1916 of a single external bow torpedo tube. It created instability and was not a success. Plus the single engine meant a lack of redundancy in case of a breakdown. The crew had to “sail they way back” if it happened. This was the same issue as for the UB-I types, but this mattered little as these small boats were setup for short missions of a couple of days or more.

Amidship section of UC-5 moving to New York City (NARA top, CC Central Park 1917 below)

Powerplant

Propulsion while surface relied either on a 4-cylinder four-stroke Daimler RS166 diesel engine, 90 PS (66 kW; 89 bhp) on the UC 1 series or a 80-horsepower 6-cylinder Benz diesel engine, 80 PS (59 kW; 79 bhp) diesel engine for the UC-11 serie. While underwater they relied on the same 175 hp SSW (Siemens Schuckert) electric motor. The propulsion system was meant for a single shaft and at its tip for a three-bladed bronze propeller, 1.8 m (6 ft) in diameter with a 0.43 m (1.4 m) pitch. This delivered on average a top speed of 6.2 knots surfaced and 5.22 knots submerged. It was tested in case of diesel breakdown a surface run with the electric motor and it can be as much as 7.5 knots.
It varied between series:
UC-1 – UC-10 were capable of 6.20 knots (11.48 km/h; 7.13 mph) surfaced and 5.22 knots (9.67 km/h; 6.01 mph) submerged
UC-11 – UC-15 were capable of 6.49 knots (12.02 km/h; 7.47 mph) surfaced and 5.67 knots (10.50 km/h; 6.52 mph) submerged.
The range was 780 nautical miles nominally at 5 knots surfaced, but it also varied between series:
For vessels built at Vulcan shipyard (UC-11 through UC-15): Surface range was 910 nautical miles max or 80 nmi (1,440 km; 900 mi) at 5 knots (9.3 km/h; 5.8 mph) surfaced and 50 nmi (93 km; 58 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged.
For vessels built at Bremen (UC-11 – UC-15) it was 910 nmi (1,690 km; 1,050 mi) at 5 knots (9.3 km/h; 5.8 mph) surfaced and 50 nmi (93 km; 58 mi) at 4 knots (7.4 km/h; 4.6 mph) submerged.
All these carried only 3.5 tons of diesel fuel. The electrical power was stored in batteries, in total 112 cells split between two wells, with a total capacity of 4,000 Ah, providing 3 hours of submerged operation at full load. As for diving the UC-I as said above had two internal main ballast tanks, split in separare units fore and amidship. Maximum diving depth was 50 meters (165 feet), and diving time ranged from 23 to 36 seconds.

Armament

The sole armament, past the liquid cooled 8 millimetres (0.31 in) machine gun (to be brought up and fixed on a pintle) with a supply of 150 rounds, and small arms on board as seen above, there were the twelve UC 120 mines carried. They were stored in six 100 mm or 39 inches diameter mine shafts as tall as the hull, as they weere reloaded by the top hatches and dropped by bottom openings (they were open to the sea). They were held in place by brackets released by simple mechanical wires. There was no access and nothing usable for the depth setup. Indeed, the depth setting was determined per mission, before the miens were loaded down and stowed in the tubes. So once the U-boat departed, if the the target zone could not be altered or reached, the mission was aborted, unless there was an alternative site that required the same depth setting.

These UC-120 mines were moored contact naval models specifically designed the Type UC I submarine and Type UC II. They had a main explosive charge of approximately 120 kg (260–290 lbs) of wet guncotton or TNT. To detonate, they had chemical firing horns (acid-lead / Hertz horns). In Diameter they were 80 cm (31.5 in), built to fit standard 100 cm (39 in) vertical submarine mine chutes. Explosive Load was c120 kg (264–290 lbs) of wet guncotton or TNT. Mooring Depth was Adjustable up to roughly 100 meters (328 ft) of cable length. They were dropped via gravity from their vertical launch tubes via the bottom opening open to the sea. For survivor boats, they were replaced mid-1915 by the larger UC 200 mine and subsequent variations.

⚙ UC-I specifications
Displacement	168 t surfaced/light, 182-183 t (180 long tons) surbmerged
Dimensions	33.99 (29.62/29.81 m PH) x 3.15m. Height 6.30 (111 ft 6 in x 10 ft 4 in x 20 ft 8 in)
Propulsion	4-cyl. Daimler RS166 diesel or 6-cyl. Benz engine 80/90 PS, SSW Motor 175PS
Speed	6.2-6.5 kts surfaced, 5.22-5.67 kts submerged
Range	See notes: 780-910 nm surfaced, 50 nmi surbmerged
Armament	12x UC 120 mines, see notes
Max depth	50 m (160 ft)
Crew	14 men

Career of the UC-I

Of the 12 boats made, only UC-5 and UC-8 survived the war. They all operated from Zeebrugge during the war and losses were heavy indeed with most striking mines (sometimes their own), some grounded in treacherous estuaries or coastal changing sand banks. The loss by mines came from the system of setup mines in the wet tubes, inaccessible while at sea with mine fuzes operational. This clearly showed as an unsafe practice that led to the loss of several vessels. When the better UC-II entered service, the UC-I were disassembled and shipped back inland for operations in the Baltic and Mediterranean.

Indeed, both the fleet command and crews were highly skeptical regarding the UC-I capabilities, small, slow and unsafe. But in service, they proved them wrong. They had been throughly underestimated and proved to very useful assets against allied and in partcular British shipping when Germany still adhered to international maritime law and regular U-Boat still had to stop and board, inspect ships under prize rules. Prior to unrestricted submarine warfare, covertly laid mines was the only method available to blockade the British Isles. Although all but two UC I-class were lost their record was impressive and equalled the small UB-I, their torpedo-carrying cousins: Collectively, they destroyed 272 ships totaling 346,628 GRT and 17 warships totaling 30,203 tons. Additionally, 35 ships (134,996 GRT) and 3 warships (5,894 tons) were damaged.

Their effectiveness was hampered by limitations inherent in carrying mines outside the pressure hull. Inaccessible while at sea and laid at a depth preset before departing left commanders with precision navigation skills that were quite to high standards. Mines were frequently laid in waters either too shallow, easy to spot and sweep, or too deep, so the ships passed safely over. Another drawback was their insufficient speed surfaced and submerged making it difficult to contend with strong currents of the Strait of Dover and in general, sluggisgh when penetrating estuaries, their privileged target.
Both the shortcomings of the UC-Is and massive successes led to the development of new, larger, and improved submarine classes UC II and UC III. The latter were recoignized postwar of among the very best in their trade, inspiring copycats, and a base on which the future WW2 U-Boats were designed, like the Type VII.
Note: These logs are simplified. There might be extra details in future updates.

S.M.S. UC-1

SM UC-1 was ordered on November 23, 1914, as part of the wartime fleet expansion program and prototype for the UC I class. She was laid down at Vulcan shipyard in Hamburg under yard number 45 (Werk 45), launched on April 26, 1915, commissioned on July 5, 1915. She had eight commanding officers in her career. First she was in the Flanders Flotilla, making an astonishing 80 sorties, primarily off the east coast of the British Isles and English Channel. Her minefields claimed 36 merchant vessels (totaling 55,869 GRT), 5 warships (totaling 3,067 tons), damaging 7 merchant vessels (totaling 45,844 GRT) setting a record. She was lost with all hands on July 19, 1917, probably a mine near Nieuwpoort in West Flanders.

S.M.S. UC-2

SM UC-2 was built at Vulcan, Hamburg, yard number 46, launched on May 12, 1915, commissioned on May 17, 1915. Her only commanding officer was Kapitänleutnant Karl Mey. Her service with the Flanders Flotilla wa sshort: SM UC-2 only performed two unsuccessful minelaying missions (no kills) off the east coast of Great Britain. Overdue she is assumed lost on June 30, 1915 after one of her own mine detonated while laying a minefield near Lowestoft. Shortly after, the wreck was examined by Royal Navy divers as it was in shallow waters. She was raised, studied, then put on public display to demonstrate the effectiveness of British naval operations.

S.M.S. UC-3

SM UC-3 was built at Vulcan, Hamburg, yard number 47, launched on May 28, 1915, commissioned on June 1, 1915. She had had three commanding officers, starting with the Flanders Flotilla. There, SM UC-3 made a total of twenty-nine sorties, moslty off the east coast and Channel. Her mines claimed some nineteen ships for 29,021 GRT and three warships (1,571 tons) and damaged two (1,909 GRT). The was lost with all hands on May 27, 1916, after striking a British mine north of Zeebrugge, on the path of these submarines.

S.M.S. UC-4

SM UC-4 was built at Vulcan, Hamburg, as Werk 48, launched on June 6, 1915, commissioned on June 10, 1915. She had a long career with thirteen commanding officers. Between the Baltic Flotilla and Flanders Flotilla, she performed 73 sorties, moslty off the east coast and her mines claimed 32 ships (36,391 GRT), 4 warships (8,397 tons) plus 2 damaged (9,441 GRT). She survived the war, being scuttled on October 5, 1918, off the coast of Flanders due to the German evacuation from Belgium. She was scrapped postwar by the Belgians given her general state.

S.M.S. UC-5

SM UC-5 was built at Vulcan, Hamburg under Werk 49, launched on June 13, 1915, commissioned on June 19, 1915. Her existence was long, but her career was short, she only had two commanders. In the Flanders Flotilla, she performed 29 sorties, east coast of the British Isles and Channe and her mines claimed 28 ships (36,126 GRT), two warships (1,105 tons) damaging 7 ships (20,262 GRT). On April 27, 1916, SM UC-5 ran aground near Harwich. She could not be unstuck, and had been spotted so her commander knew the RN were about to rush there. So he ordered her scuttled by explosive charges, and abandoned. Stranded, they were taken prisoner. The submarine was then raised and repaired, studied and then exhibited to the public. She even started a propaganda tour, going to the United States to draw attention to the war, and to Canada until 1918, being scrapped after the war.

S.M.S. UC-6

SM UC-6 was built at Vulcan, Hamburg, as Werk 50, launched on June 20, 1915, commissioned on June 24, 1915. She had a long career with six successive commanding officers, starting with the Flanders Flotilla, making for a record 89 combat sorties off the east coast and Channel and claiming 54 vessels (63,319 GRT). One was a big prize, the liner Maloja (12,431 GRT) and a 810t auxiliary warship, damaging 8 more ships totaling 33,104 GRT, another 810 tons warship. SM UC-6 sank with all hands on September 27, 1917, likely after being struck by a defensive mine in the Thames Estuary, or one of a fellow U-Boote, off-the-chart.

S.M.S. UC-7

SM UC-7 was built at Vulcan, Hamburg, under Werk 51, launched on July 6, 1915, commissioned on July 9. She had two commanders in service, starting with the Flanders Flotilla. There, she performed 34 combat sorties on the east coast and Channe, claiming 31 ships (45,734 GRT) with her biggets kill being the Dutch passenger Koningin Emma (9,181 GRT) and second the 3,520 tons light cruiser HMS Arethusa, flagship of Harwich Force’s Commodore Reginald Tyrwhitt. She aslso damaged two (6,151 GRT) but was loist with all hands on July 5, 1916, likely after striking a British barrage mine north of Zeebrugge.

S.M.S. UC-8

SM UC-8 was built at Vulcan, Hamburg under Werk 52, launched on July 6, 1915, commissioned on July 15. She had two commanding officers in services and in her maiden voyage on November 4, she ran aground in Dutch territorial waters and was interned by local authorities befire any operational mission. She was purchased by the Dutch government as a neutral nation, and entered service with the Royal Netherlands Navy or Koninklijke Marine in March 1917. She became Hr.Ms. M1 and served until 1931 until sold for scrap in 1932 ads the first Dutch minelaying submarines. Others will follow. She was the only UC I-class surviving to the interwar.

S.M.S. UC-9

SM UC-9 was built at Vulcan, Hamburg under Werk 53, launched on July 11, 1915, commissioned on July 15. She had a short career under Lieutenant Paul Schürmann in the Flanders Flotilla. She made just two minelaying missions without success. She then sank with all hands off Harwich on October 21, 1915, likely due to the premature detonation of one of her own mines.

S.M.S. UC-10

SM UC-10 was built at Vulcan, Hamburg under Werk 54, launched on July 15, 1915, commissioned on July 17. She had a long career with five commanding officers starting with the Flanders Flotilla, for a total there of 30 combat sorties off the east coast and claiming some sixteen ships (30,406 GRT) sunk, two small warships (598 tons), five damaged (16,627 GRT). She was lost with all hands on August 21, 1916, after being torpedoed by HMS E54, likely surfaced by night to reload and rest.

S.M.S. UC-11

SM UC-11 was built at AG Weser shipyard, Bremen (lead boat) under yard number 225 or “Werk 225”. She was laid on January 26, 1915, launched on April 11, commissioned on April 23, under just three months. She had a long career and ten commanding officers. With the Flanders Flotilla, she made 83 combat sorties off the east coast bu “only” claimed 25 vessels sunk (33,198 GRT), two warships (510 tons); three damaged, one merchant 378 GRT and two warships 5,084 tons, including the British 4,219 tons C-class light cruiser HMS Conquest. SM UC-11 sank on June 26, 1918, after striking a mine near Harwich and the commanding officer on watch on the CT was the only one that survived, thrown off board.

S.M.S. UC-12

SM UC-12 was built at AG Weser Bremen under Werk 226, laid on January 27, 1915, launched on April 29, commissioned on May 2. She had had three commanding officers but insted of the Flanders Flotrilla she was sent by rail in sections to the Adriatic, assembled and nominally incorporated into the Kaiserliche und Königliche Kriegsmarine as “U-24”. The flag and overall command were Aiustro-Hungarian but the crew was German. She operated from Pola, making seven combat sorties mostly to block the few passages known to be used by entente ships in the Strait of Otranto. This claimed 6 ships sank (3,289 GRT). Herself sank on March 16, 1916, by one of her own mines near Taranto. Raised and refitted by the Italians, she served as “X 1” until 1919, studied and helping designing minelaying subs in the RM, before being scrapped.

S.M.S. UC-13

SM UC-13 was built at AG Weser Bremen under Werk 227, laid on January 28, 1915, launched on May 11, commissioned on May 15. Her only commander was Kapitänleutnant Johannes Kirchner. Like her sister UC-12 she was carried in sections to the Adriatic, and became U-25 in Austrian service. But she was not intended to operated from Pola unlike her sister. She was shipped to the Bulgarian coast and attacked Constantinople, making three combat patrols in the Aegean and Black Seas. UC-13 sank three ships (387 GRT) damaged one (1,280 GRT) until she was lost on November 29, 1915, after running aground east of the Bosphorus, finished off by Russian destroyers.

S.M.S. UC-14

SM UC-14 was built at AG Weser, Bremen under Werk 229, laid on January 28, 1915, launched on May 13, commissioned on June 5. She had six commanding officers and like her sisters was carried in sections to the Adriatic, incorporated into the Austro-Hungarian Navy as U-18. She was in the Pola Flotilla and from January 1917 after lackluster results, sent back in section to serve in the Flanders Flotilla, making 38 combat sorties between the Adriatic and North Sea and caliming 14 ships sunk (8,182 GRT), two warships (14,107 tons) including the biggest prize of them all, the battleship Regina Margherita in the Adriatic. This alone deterred the entente into sending large warships and concentrate on smaller ones. UC-14 sank with all hands on October 3, 1917, after striking a British mine near Zeebrugge.

S.M.S. UC-15

SM UC-15 was ordered on November 23, 1914 as the last ship in class, ordered from AG Weser, Bremen under Werk 230, laid on January 28, 1915, launched on May 19, commissioned on June 28. She had two commanders, being transported by rail to Pola, Adriatic and operate under Asutrian flag as U-19. She was however soon moved to the U-boat division in Constantinople, completing 8 sorties in the Black Sea but only sinking two ships (874 GRT) and one 350 tons warship. She was lost with all hands somewhere after November 13, 1916, assumed by its own mine while laying a minefield at the mouth of the Danube.