During World War II he worked for the Australian government, helping to decrypt Japanese communications. In January 1940, with the encouragement of the Australian Army, he, together with some colleagues at the University of Sydney, began to study Japanese codes. The others were the mathematician Richard Lyons and the classicists Arthur Dale Trendall and Athanasius Treweek. By this time Room had already begun learning Japanese under Margaret Ethel Lake (1883-?) at the University of Sydney. In May 1941 Room and Treweek attended a meeting at the Victoria Barracks in Melbourne with the Director of Naval Intelligence of the Royal Australian Navy, several Australian Army intelligence officers and Eric Nave, an expert Japanese cryptographer with the Royal Australian Navy. As a result it was agreed that Room's group, with the agreement of the University of Sydney, would move in August 1941 to work under Nave at the Special Intelligence Bureau in Melbourne. On 1 September 1941, Room was sent to the Far East Combined Bureau in Singapore to study the codebreaking techniques used there. After the outbreak of war they were working for FRUMEL (Fleet Radio Unit Melbourne), a joint American-Australian intelligence unit, but when Lieutenant Rudolph Fabian took over command of FRUMEL and particularly when, in October 1942, FRUMEL was placed under direct control of the US Navy, civilians such as the member of Room's group were found surplus to requirements and returned to their academic posts. Peter Kornicki, Eavesdropping on the Emperor: Interrogators and Codebreakers in Britain's War with Japan (London: Hurst & Co., 2021), pp. 209-211, 216-7.Peter Donovan, and John Mack, ‘Sydney University, T. G. Room and codebreaking in WW II’, Australian mathematical society gazette 29 (2002): 76-85, 141-8.
