In 1920, his father financed a trip to Hollywood in hopes that Day would find a job in the film industry.
He personally worked on selected films such as How Green Was My Valley (1941), for which he won his third Academy Award.
During World War II, Day independently developed camouflage designs and relief mapping techniques.
[1] Once in the service, he devised a technique to make relief models of assault landing sites out of mud and other available materials.
Day won seven Academy Awards for Best Art Direction:[3][4] He was nominated in the same category for a further 13 films: