The de Havilland Vampire, or DH.100, was the second jet engined aircraft commissioned into the Royal Air Force during World War II (the first being the Gloster Meteor), although it did not see combat in that conflict. After the war, it served with the front-line RAF until 1955. It also served with foreign air forces, including those of Australia, Canada, Finland, France, India, Ireland, New Zealand, Norway, Sweden, Rhodesia and Switzerland. Almost 4,400 Vampires were built, a quarter of them under licence. The Vampire began as an experimental aircraft, unlike the Gloster Meteor which was always specified for production. Under specification E.6/41, design work on the DH-100 began at the de Havilland works at Hatfield in mid-1942, two years after the Meteor.