Henderson was one of the first two salaried Air Ministry artists, along with Paul Nash, appointed in early 1940. He was sent to RAF locations in Scotland but was frustrated to find that William Rothenstein independent activities, painting portraits of airmen (q.v.) had "forestalled" him and caused confusion among the air force personnel. As a result Henderson concentrated on "views and hangars". His letters are lively and contain many references to specific works, often with comments or descriptions. He occasionally refers to Paul Nash.
Henderson felt somewhat rushed by Peake of the Air Ministry (whom he refers to as "Blondie"), and was disappointed that his appointment was not renewed at the end of six months, as he had planned schemes of works for a year. He asked that he might be able to continue to work in some way.
Henderson often writes regarding photographs of his works, being particularly concerned that the pictures might be bombed without a record remaining of them. He also suggested that prints (of his own work and others') be made available for sale to airmen.