SM UB-47 - Design and Construction

Design and Construction

The German UB II design improved upon the design of the UB I boats, which had been ordered in September 1914. In service, the UB I boats were found to be too small and too slow. A major problem was that, because they had a single propeller shaft/engine combo, if either component failed, the U-boat became almost totally disabled. To rectify this flaw, the UB II boats featured twin propeller shafts and twin engines (one shaft for each engine), which also increased the U-boat's top speed. The new design also included more powerful batteries, larger torpedo tubes, and a deck gun. As a UB II boat, U-47 could also carry twice the torpedo load of her UB I counterparts, and nearly ten times as much fuel. To contain all of these changes the hull was larger, and the surface and submerged displacement was more than double that of the UB I boats.

The Imperial German Navy ordered UB-47 from AG Weser on 31 July 1915 as the final boat of a series of six UB II boats (numbered from UB-42 to UB-47), and the last UB II submarine numerically. UB-47 was 121 feet (37 m) long and 14 feet 5 inches (4.39 m) abeam. She had a single hull with saddle tanks and had a draft of 12 feet 2 inches (3.71 m) when surfaced. She displaced 305 metric tons (336 short tons) while submerged but only 272 metric tons (300 short tons) on the surface.

The submarine was equipped with twin diesel engines and twin electric motors—for surfaced and submerged running, respectively—that drove twin propeller shafts. UB-47 had a surface speed of up to 8.82 knots (16.33 km/h) and could go as fast as 6.22 knots (11.52 km/h) while underwater. The U-boat could carry up to 27 metric tons (30 short tons) of diesel fuel, giving her a range of 6,940 nautical miles at 5 knots (12,850 km at 9.3 km/h). Her electric motors and batteries provided a range of 45 nautical miles at 4 knots (83 km at 7.4 km/h) while submerged. UB-47 was equipped with two 50-centimeter (19.7 in) bow torpedo tubes and could carry four torpedoes. The U-boat was also armed with an 88 mm/26 (3.5 in) deck gun and an 8 mm (0.31 in) machine gun.

UB-47 was laid down by AG Weser at its Bremen shipyard on 4 September 1915. As one of six U-boats selected for service in the Mediterranean while under construction, UB-47 was broken into railcar-sized components and shipped overland to the Austro-Hungarian port of Pola. Shipyard workers from Weser assembled the boat and her five sisters at Pola, where she was launched on 17 June.