Bomber Command acquired B-29 Superfortresses – known to the RAF as Boeing Washingtons – to supplement the Avro Lincoln, a development of the Lancaster. The first jet bomber, the English Electric Canberra light bomber, became operational in 1951. Some Canberras remained in RAF service up to 2006 as photo-reconnaissance aircraft. The model proved an extremely successful aircraft; Britain exported it to many countries and licensed it for construction in the United States and in Australia. The joint US-UK Project E was made nuclear weapons available to Bomber Command in an emergency, with the Canberras the first aircraft to benefit. The next jet bomber to enter service was the Vickers Valiant in 1955, the first of the V bombers.