In 1935, Britten began writing incidental music for documentary films produced by the General Post Office (GPO), which led to further requests for incidental music from the Group and Left Theatres. Such work was highly beneficial. Britten developed a technique for writing music of expressive immediacy often for restricted forces, a technique that he could exploit subsequently when he turned to opera. Another advantage was his meeting and friendship with W. H. Auden, with whom he collaborated on several projects (Coal Face, 1935, Night Mail, 1936, both GPO; and The Ascent of F6, 1937, Group Theatre with Christopher Isherwood). The bitter irony heard in the orchestral song cycle, Our Hunting Fathers (Auden, 1936), and Ballad for Heroes for tenor, chorus and orchestra (Auden/Swingler, 1939) can be traced in part to Britten's developing political and social consciousness at the hands of Auden, although the latter's attempts to accelerate Britten's personal development met with little success. Auden's emigration to the United States in January, 1939 was, however, an important factor in prompting Britten to follow suit the following April.
Britten's two-and-a-half-year residence in the United States (prefaced by a short visit to Canada) was a period of liberation. The grief occasioned by the deaths of his parents was objectified in the Sinfonia da Requiem (1940), dedicated to their memory, and Britten's commitment to Pears was consummated. Two song cycles, Les Illuminations (Rimbaud, 1939) and the Seven Sonnets of Michelangelo (1940), the latter Britten's first cycle written for Pears, mark the arrival of musical maturity, although the opera, Paul Bunyan (Auden, 1941) was not a success. The chance reading of an article by E. M. Forster on Suffolk poet George Crabbe not only led Britten to realize how essential his native surroundings in Suffolk were to his well-being, but also provided him with the subject matter for Peter Grimes, the writing of which was facilitated by a $1,000 commission from the Koussevitzky Foundation. He returned to England in 1942, completing the Hymn to St. Cecilia (Auden) for unaccompanied chorus and A Ceremony of Carols en route. On arrival, Britten registered as a conscientious objector and was subsequently exempted from military service on condition that he took part in concerts for the Council for the Encouragement of Music and the Arts (CEMA).