The British GPO Film Unit was directly responsible for some of the most significant developments in documentary film thanks to the work produced by such visionaries as John Grierson. Renamed the Crown Film Unit in 1940, the office became a central locus for the production of propaganda during British involvement in World War II. Humphrey Jennings was among the filmmakers who produced films for this department. His short film Listen to Britain is generally regarded as his masterpiece, chronicling a day in the life of Britain during wartime. Although the content is drawn from everyday life, the film is romantic in tone, celebrating the spirit of the British people amidst hardship. In Fires Were Started, Jennings uses reenactments to capture the intensity of the individual struggles during this trying period, and pays tribute to the men and women of the Auxiliary Fire Service, who held London together amidst the devastation of the Luftwaffe bombing raids. Filmmaker Lindsay Anderson wrote in a 1954 Sight and Sound article that Jennings was the only true poet the British cinema had yet produced. Despite the challenges of war, Jennings presents an interconnected world of idealists determined to overcome oppression.