Type I submarine

The Type I U-boat was the first post–World War I attempt to produce an oceangoing submarine for Nazi Germany's Kriegsmarine. The type was based on the Spanish Type E-1 and Finnish CV707, which were both designed by Ingenieurskantoor voor Scheepsbouw. Only two Type IAs were built. They were not a successful design : due to its single rudder they had a large turning circle and were not very manoeuvrable. The gravity center of the U-boat was too forward so on the surface the type I had its propellers exposed when she was pitching. Whilst submerged there were problems with depth keeping and stability as air bubbles in the fuel tanks wobbled back and forth. Diving was very slow: at full speed and with six tons of negative buoyancy it took forty seconds to reach ten metres depth. As a result, the type was discontinued and a new type IX class oceangoing U-boats was designed.

Service history
Constructed by Deschimag in Bremen, the first Type IA was launched on 14 February 1936. The two boats produced, GS U-25 (1936) and GS U-26 (1936), were primarily used as training vessels and for propaganda purposes to fly the Nazi flag. In 1940, the boats were called into combat duty due to the shortage of available submarines. Both boats experienced short, but successful combat careers. U-25 participated in five war cruises, sinking eight enemy ships. On 3 August 1940, while on a mine laying mission near Norway, U-25 struck a mine and sank with all hands on board.

U-26 carried out eight war cruises, sinking three merchant ships on its first mission laying mines. On its second war cruise it became the first U-boat during World War II to enter the Mediterranean Sea. U-26 participated in three other successful war patrols, sinking four additional merchant ships. On its eighth war cruise the boat sank three merchant ships and damaged another ship the next day. The attack on this ship led to severe depth-charging by two British warships, including HMS Gladiolus (K34). Unable to dive, U-26 was forced to surface where she was bombed by a Sunderland flying boat. The crew scuttled the submarine and were rescued by Allied warships.

List of Type I submarines

 * GS U-25 (1936)
 * GS U-26 (1936)