Type UB II submarine

The design of Type UB II addressed many of the problems apparent in the preceding Type UB I class. The Type UB I had been too small and underpowered, it was not fast enough to chase fleeing merchants and it had not enough power to master the strong currents in the English Channel. When the single diesel broke down, the U-boat was helpless. The Type UB I did not have a deck gun to stop merchants.^[1]

The Type UB II boats featured a two-shaft drive with a much larger battery capacity and larger engines. Storage batteries were placed forward of the central diving tanks to compensate for the much heavier engine installation. Type UB II U-boats retained the two bow torpedo tubes of the Type UB I, but could also store two reloads internally. The torpedo tubes were installed one above the other to allow for a bow design that would create optimal surface efficiency. A deck gun was installed before the conning tower. The weight of the boat was increased to 270 tons of surface displacement to accommodate these improvements. Saddle tanks were fitted to the sides of the pressure hull to allow greater fuel storage area. The resulting larger beam meant that these U-boats were not transportable anymore by rail as the preceding Type UB I, but eventually some Type UB II were transported by rail to the Mediterranean Sea by disassembling them in longitudinal sections fitting the railroad gauge. Other improvements over the preceding Type UB I included forward hydroplanes, a second periscope operated from the central control room and a two masted wireless aerial.^[2]

On 30 April 1915, six Type UB II ( UB-18 - UB-23 ) were ordered from the Blohm & Voss shipyard in Hamburg and one day later a further six ( UB-24 - UB-29 ) were ordered from AG Weser in Bremen. The main reason for building smaller coastal submarines rather than large fleet submarines, was the building time. A fleet submarine took more than one year to build which implied a risk that they would be completed only after the end of the hostilities, whilst these coastal submarines were expected to be delivered before the end of 1915. But when it became apparent that the war would last well into 1916, eightteen more Type UB II were ordered on 27 July 1915: UB-30 - UB-41 were ordered from Blohm & Voss, but were built by Reiherstieg shipyard as subcontractor from Blohm & Voss, and UB-42 - UB-47 were ordered from AG Weser.^[2]

In August 1915 the Austro-Hungarian Navy acquired a licence from AG Weser to build Type UB II U-boats. For political reasons the building programme had to be split between the two components of the Austro-Hungarian empire: U-27 and U-28 were ordered from the Cantiere Navale Triestino in Pola which had an Austrian affiliation, and U-29 - U-32 from the Danubius yard in Trieste. which had a Hungarian affiliation. A further two U-boats were ordered from the Cantiere Navale Triestino in 1916: U-40 was ordered on 16 January and after the loss of U-6, U-41 was ordered as a substitute on 28 August. These U-boats were known as the U-27-class.^[3] Because U-41 had the spare Grazer diesel engines of U-6 installed, she was 0.8 m (2.6 ft) longer, displaced 7 t (6.9 long tons) more on the surface, and 14 t (14 long tons) more submerged, than her sister ships.^[4]

The four batches of German-built Type UB II U-boats had small variations in overall length, beam, draft and displacement. For all boats, the pressure hull had a length of 44.5 m (146 ft) and a maximum diameter of 4.70 m (15 ft 5 in). Constructional diving depth^[a] was 50 m (164 ft 1 in).^[6] They all had a complement of two officers and twenty-one men.^[7] For submerged propulsion, all boats had two 100 kW (136 PS; 134 shp) Siemens-Schuckert electric motors, which gave a range of 45 nmi (83 km; 52 mi) at 4 knots (7.4 km/h; 4.6 mph). Diesel engines for surfaced propulsion came from three different producers and the yards had to install what was available. Daimler and Körting produced a six-cylinder, four-stroke RS206 engine providing 142 brake horsepower (106 kW), Benz produced the six-cylinder, four-stroke DS25u which provided 135 bhp (101 kW).^[8]

All German-built Type UB IIs had two 50 cm (20 in) bow torpedo tubes with two internal reloads, and UB-34, UB-35 and UB-41 had two extra external above-water torpedo launchers. UB-27, UB-34, UB-35 and UB-41 could also carry fourteen mines. UB-21, UB-22, UB-23 and UB-24 could be armed with mines until 1916-1917, and UB-26 received the capability to carry mines only in 1916-1917.^[9] The first Type UB II U-boats had a 5 cm SK L/40 deck gun, but later U-boats had a 8.8 cm SK L/30 installed. Some of the U-boats with a 5 cm gun had it later replaced by a 8.8 cm gun; in 1916 in preparation of a renewed U-boat offensive, all Type UB II U-boats of the Flanders U-boat flotilla had a 8.8 cm gun installed so that they were better equipped to attack shipping according to the Prize rules.^[10]

The Austro-Hungarian Type UB II U-boats had a complement of five officers and fourteen men. These U-boats were equipped with two torpedo tubes and two torpedo reloads of the smaller 45 cm (18 in) size. They were also equipped with a 75 mm/26 (3.0 in) deck gun and an 8 mm (0.31 in) machine gun ^[4]

There were thirty Type UB II submarines commissioned into the German Imperial Navy and eight into the Austro-Hungarian Navy. Two German built boats, the UB-43 and UB-47 were sold to Austria-Hungaria on 30 july 1917, transported by rail to Pola at the Adriatic Sea, and were commissioned in the Austro-Hungarian Navy as U-43 and U-47 respectivily.^[13]