The enactment of the Second Naval Law represented an ambitious plan to double the size of the German fleet, but with the British Royal Navy having long been the world’s dominant maritime force Germany’s naval expansion was perceived as a direct challenge to British supremacy.

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.