Mike Napier the author says;

The Vickers Wellington is the great unsung hero of World War II. One of only two aircraft types that served in the front line of the RAF throughout World War II and remained in production throughout the conflict (the other was the Supermarine Spitfire), the Vickers Wellington was the mainstay of Bomber Command for the first three years of the war and became the workhorse of Coastal Command service, played a vital role during the Middle East and Mediterranean campaigns and also contributed greatly to operations in the Far East theatre. While everyone has heard of the Wellington, few realise its incredible versatility or the vitally important part that it played in RAF operations in all of the theatres of war. I could have written about the Wellington in any of its many theatres or roles, but I decided to concentrate on the Wellington units within Bomber Command. Why? Because the Wellington holds a unique and fascinating place in Bomber Command history.