Ayer was influenced by the service of veterans in his family and by reading books, such as Belton Y. Cooper's Death Traps, about American armored units in World War II and the high casualty rates suffered by tank crews in Europe.
Ayer baseouse no servizo de familiares seus e na lectura de libros, como Death Traps de Belton Y. Cooper, para representar as unidades estadounidenses na segunda guerra mundial e as grandes baixas sufridas polos tripulantes de tanques en Europa.