A brilliant linguist with infantry and Intelligence Corps experience from 1914–18, proven anti-fascist credentials and a scepticism about the Soviet Union, Lucas was one of the first academics recruited by the Foreign Office – on 3 September 1939 – to Bletchley Park. He was one of the original four members of Hut 3, whose organisation he set up, and from March to July 1942, when the Hut was run by committee, acting head. He remained a central figure there, working throughout the war on the Enigma decodes as translator, intelligence-analyst and (from July 1942) head of the Research Section, "3G" [:Hut 3 General Intelligence], on the busy 4 p.m. to 1 a.m. shift. His main activities in "3G" were cracking Axis covernames and covernumbers in decodes, analysing German "proformas" (supplies and ammunition returns), and writing general intelligence papers.