Lerew was posted to RAAF Overseas Headquarters, London, in December 1943. He travelled via the United States, meeting film stars Bing Crosby, Bob Hope, and Dorothy Lamour on the set of "Road to Utopia" at Los Angeles in February 1944. In London, he undertook study of RAF and USAAF methods of operations, as well as diplomatic duties. Of the invasion of France on 6 June 1944, he wrote: "There has been no rejoicing. A hushed quietness has descended over London and all of England. Most people have relatives in it, and there is only one wish: that is, that it will end quickly. It is depressing to be playing no part in it." Later in the year, Lerew was invested with his Distinguished Flying Cross by King George VI at Buckingham Palace. He returned to Australia in early 1945, and married Laurie Steele, the Australian-born widow of a Royal Air Force night-fighter pilot, having met her when he was stationed in England. The couple had two daughters, but eventually divorced. In March, Lerew took part in the investigation into the crash of a Hudson carrying Major General George Vasey; he determined that the pilot's lack of experience in instrument flying had been a factor, and recommended further such training for RAAF flight crew. Promoted group captain, he formed the Directorate of Flying Safety in June 1945 and served as its inaugural Director. Believing that the promotion of flying safety in the RAAF cut across both administrative and operational spheres, and aware of the notorious feud between the service's two senior officers, Air Vice Marshals George Jones and Bill Bostock, Lerew had proposed that the new directorate be placed squarely under the auspices of Jones as Chief of the Air Staff, with authority to demand free access to information from all other directorates.