On February 4, 1915, Admiral Hugo von Pohl of the German High Seas Fleet warned that ‘every enemy merchant vessel’ in British waters would be targeted and that ‘it may not always be possible to prevent attacks on enemy ships from harming neutral ships’.

A British party of Lieutenant Francis Fasson, Able Seaman Colin Grazier, and canteen assistant Tommy Brown, boarded the slowly-sinking submarine after it had been damaged by depth charges and retrieved the Enigma codebooks and all the current settings for the U-boat network.