The RAF entered World War II with no heavy bomber of its own in service; the biggest available were long-range medium bombers such as the Vickers Wellington, which could carry up to 4,500 pounds (2,000 kg) of bombs.
Royal Air Force påbegyndte 2.verdenskrig uden at have tunge bombefly i tjeneste; de største var mellemstore langdistance bombefly som Vickers Wellington, som kun kunne bære op til 2.000 kg bomber.