U 31 Design

U 31 was been considered as a matured design and was so much successful that it was been used throughout the whole war unchanged in it's core design, just with many improvements in every new series. U 31 belonged already to a generation of submarines that were equipped with diesel engines, thus fully suited for the war, unlike their predecessors which were equipped with kerosene engines what was been seen, by the admiralty, as unsuitable for real war duty. At the beginning the diesel engines suffered from lots of teething problems and this new U-Boats suffered regular engine breakdowns, and even had to cancel maneuvers sometimes. But at the beginning of the war the problems were solved and they were ready for the war. But the crews of this new boats were unexperienced by the beginning of the war.

The engine breakdowns increased during the war again. This was not because of a quality lack of the engine design but because of the growing material shortage caused by the sea blockade that have forced the yards to use materials that were not suitable to be manufactured in to an engine. This led often to heavy engine breakdowns and made it sometimes a big challenge to the crew to return home. Besides the increasing break downs, were the u-boats forced more and more to decrease their maximum speed. Later it was often even not possible to increase the speed to full and from the 17 knots top speed only 13 were left that could be hold for only a short time and 11 knots as a permanent maximum speed( U 96 ).

Periscopes

U31 was equipped with one attack and one air observing periscope with zoom settings of 1,5x and 6x.

Armament

The pre war designs didn't had so much torpedos aboard. Only 6 torpedos could be carried inside U31. During the war however the demand for more torpedos grew higher and higher, so later in the war they started to upgrade the older boats with external pods which could carry additional torpedos( 4 external on fleet type boats ) and wherever possible additional torpedos were cramped into the torpedo rooms.

Also unusual for this advanced type is that it had no deck guns. It wasn't unusual though, for the U-Boats build before the war. Many were upgraded during the war with deck guns but U31 was M.I.A. after it left the port at 13 January 1915 under Kt.Lt.Wachendorff, one year after it was been commissioned. So it hadn't much chances for any upgrades and it didn't achieved any successes during its service time. But some sources depic it with a deck gun.

All u-boats except U 1 were additionally equipped with mchine guns and rifles.

Tower

One disadvantage of this design was the tower construction. The crew was basically exposed to the rough sea, because there were only railings that prevented that someone will falling down but didn't gave any cover from the rough sea. To remedy this canvas was spanned infront of the railings but this was a no no in enemy waters since it takes additional time to rig it away before diving. There are some indications that later it might have been upgraded with a metal entrenchment, wrapping the tower from between the periscopes and hatch till the aft end of the tower where the railings end, on the image below.

The tower of U31

Soon the most newer boats were equipped with a new tower design, where the crew stand behind a metal trench.

Here, two examples of entrenched towers( U 98/U-Deutschland).

Internal Arrangement

Another disadvantage was the internal compartment arrangement of the U-Boat. The captain for example lived in the bow torpedoroom. In case of emergency and alert he had to sprint throughout the half of the U-Boat before he can reach the control room and tower. On later designs the captains quarter was moved next to the control room so that he could reach the control room and tower immediately and not getting stuck in a mess of an emergency case.

16,4/9,7 kn