Walther Schwieger

Kapitänleutnant Walther Schwieger (1885-1917) was commander of the U-20. On 7th May 1915 he ordered the torpedoing of the RMS Lusitania.

In an alternate timeline, Schwieger did not sink the Lusitania as his ship was hijacked by his prisoner, the Doctor, so that he would bring him back to his TARDIS. (BFA: The Sirens of Time)