The Type UC II submarine was a class of coastal minelaying U-boats designed and built for the Imperial German Navy during World War I. They were a significant improvement over the preceding Type UC I in armament, range and seaking abilities. Construction began in 1915 and by mid-1917 64 Type UC II had been delivered by five shipyards in ten different batches, which had variations in dimensions and performance. By the end of the war, 46 Type UC II were lost. The Type UC II was a very successful design combining torpedo, deck gun and mine armament with a sufficient performance and range to operate around Great Britain. A succeeding Type UC III was ordered and built in large numbers but came too late to see service in World War I.
In the summer of 1916 some restrictions were imposed on the unrestricted submarine warfare campaign, and minelaying became more significant. The Type UC I minelayer had proven its value and that U-boat design had fulfilled the expectations, but it had its limitations: The Type UC I was underpowered and had problems operating in the strong currents of the English Channel, it had only one diesel engine so when that engine broke down the boat was helpless and the lack of a deck gun and torpedo tube made it impossible to attack any enemy ship encountered whilst on minelaying mission.
In order to tackle these problems and to fulfill the extra requirement of being able to sail independently to the Mediterranean Sea instead of being disassembled and transported by rail, a much larger Type UC II was designed. The Type UC II was equipped with the same UC/200 mines as the Type UC I, and mounted the same number of inclined mine shafts going through the pressure hull. Because of the larger hull, and by raising the forward deck, these mine shafts were longer and could store three instead of two mines. In order to give the Type UC II also offensive armament, a torpedo compartment with one torpedo tube was installed on the stern after the engine compartment. As the mine shafts occupied the complete bow compartment, two bow torpedo tubes were mounted externally besides the raised mineshaft deck. A deck gun was installed between the raised foredeck and the conning tower.
Although the combination of mines, torpedo and deck gun, the extended range and increased surface speed, made this Type UC II one of the most efficient U-boat designs, there were some drawbacks: the raised forecastle made the boat more difficult to handle, especially when wind was above Force 5. This raised bow made diving also more difficult and slow, although the thirty-five to forty second diving time were considered given the circumstances. A third drawback of the raised bow was that the deck gun was awash in rough seas, and spray made watchkeeping on the conning tower difficult even in moderate weather. These problems were addressed in the subsequent Type UC III, but this type did not become operational before the end of the war.
On 21 August 1915 the first two batches of Type UC II were ordered: Blohm & Voss in Hamburg received an order for nine Type UC II - and AG Vulcan in Hamburg received an order for a further nine U-boats - , with expected delivery date between March and June 1916. After the cessation of the first unrestricted submarine warfare campaign on 19 September 1915, the way of enforcing the blockade of Great Britain shifted even more towards minelaying, and on 9 November 1915 the German Navy decided to build as many Type UC II as could be built by September 1916. Six more Type UC II - were ordered from Blohm & Voss, a further six - from AG Vulcan and AG Weser in Hamburg received an order for three U-boats - . In January 1916, the head of the German Navy Alfred von Tirpitz ordered the construction work on ships which would not be finished before October 1916, be delayed in order to free up capacity for further Type UC II construction. Five more batches were ordered on 11 January 1916: - from Germaniawerft, - from Kaiserliche Werft Danzig, - from AG Weser, - from Blohm & Voss and - from Vulcan.
All ten Type UC II batches had small variations in overall length, length of the pressure hull, draft and displacement. All Type UC II had a beam of , a complement of three officers and twenty-three enlisted men. One reason for the variations in overall length was the different form of the bow, which in early versions was rounded, whilst later versions had a sharp nose, with many boats receiving the modification from rounded to pointed bow after construction. Constructional diving depth was 50 meters (164 feet).
For surfaced propulsion, five types of six-cylinder, four-stroke diesel engines were used: Daimler produced the MU256 engine providing , Körting produced an engine providing , Benz produced the OS32 which provided and MAN produced the S6V23/34 and the S6V26/36. For submerged propulsion, the first five Type UC II batches had two combined motor/generators of each installed, whilst the last five batches had combined motor/generators. Both types were produced by Siemens-Schuckert and by Brown, Boveri & Cie as well. Combined with the variations in dimensions, these variations in propulsion affected speed and range:
Type UC II U-boats had two external torpedo tubes which could only be fired whilst submerged, and one internal torpedo tube aft. The aft torpedo compartment was very small; the two spare torpedoes had to disassembled in three parts for stowage. The external torpedo tubes had one spare torpedo each, which was also stored externally above the ballast tanks on the side, behind the torpedo tube. The bow compartment contained six mine shafts which contained three UC 120 mines each. The UC 120 was an anchored mine with contact fuzes and contained of TNT explosives. The mine shafts were open and were integrated in the pressure hull so the mines were kept in wet storage and consequently the depth setting of the mines had to be fixed before the patrol and could not be altered anymore during the patrol. As constructed, the Type UC II received a 8.8 cm SK L/30 deck gun which was in 1918 replaced with a 10.5 cm SK L/45 on some boats.
There were 64 Type UC II submarines commissioned into the Imperial German Navy.