 In autumn 1943, Milner-Barry took over as head of Hut 6, which by that time had grown to over 450 staff, Welchman having been appointed the Assistant Director of Mechanisation at Bletchley Park. He remained in charge until the end of the war, presiding over a number of technical challenges presented by the introduction of extra security devices to the German Enigma, including the Enigma Uhr and a rewireable "reflector" rotor. His entry in the Oxford Dictionary of National Biography notes that, "although he increasingly felt that Hut 6 was on the verge of losing the ability to decode Enigma, it held on until the end of the war, and this was due in no small part to his gifted leadership." The official history of Hut 6, written immediately after the end of World War II, comments on his early "most vital technical achievement" in finding cribs, and on his "administrative and diplomatic talents" in his later role as head of the section.
