Although historically in the shadow of the Gloster Meteor, the de Havilland Vampire may have been the second jet fighter to enter Royal Air Force service, but was a hugely significant aircraft in its own right. 
The first RAF aircraft capable of exceeding 500mph, the Vampire was also the first single-engined jet-powered aircraft to cross the Atlantic Ocean, marking it as one of the most important of the world's early jets. 
The FB.5 fighter bomber was the most important variant of the aircraft with 1123 aircraft built and 930 seeing service with the Royal Air Force - those destined for service overseas were designated FB.9 and had cockpit air conditioning.