Austro-Hungarian Navy submarines were also known as U-boats. U-boats are most known for their unrestricted submarine warfare in both world wars , trying to disrupt merchant traffic towards the UK and force the UK out of the war. In World War I , Germany intermittently waged unrestricted submarine warfare against the UK : a first campaign in was abandoned after strong protests from the US but in the Germans, facing deadlock on the continent, saw no other option than to resume the campaign in February The renewed campaign failed to achieve its goal mainly because of the introduction of convoys.
Instead the campaign ensured final defeat as the campaign was a contributing factor to the entry of the US in the First World War. This ultimately came to a head in May , known as Black May , in which U-boat losses began to outpace their effect on shipping.
The first submarine built in Germany, the three-man Brandtaucher , sank to the bottom of Kiel Harbor on 1 February during a test dive. Dredging operations in rediscovered Brandtaucher ; she was later raised and put on historical display in Germany.
At the beginning of the century, the German commander of the Navy Alfred von Tirpitz was building the High Seas Fleet with which he intended to challenge the supremacy of the Royal Navy. He focused on expensive battleships and there was no role for submarines in his fleet. Because speed and range were severely limited underwater while running on battery power, U-boats were required to spend most of their time surfaced, running on fuel engines, diving only when attacked or for torpedo strikes.
The more ship-like hull design reflects the fact that these were primarily surface vessels that could submerge when necessary. This contrasts with the cylindrical profile of modern nuclear submarines , which are more hydrodynamic under water where they spend the majority of their time , but less stable on the surface.
