announced on 27 January 1950 that it had agreed to acquire Boeing B-29 Superfortress bombers from the United States free under the recently passed American Mutual Defense Assistance Act. This allowed the Air Ministry to drop the development of the Sperrin. The B-29 served in the RAF under the name of the Washington B1. The RAF received its first Washington on 22 March 1950, and the eighty-seventh was delivered in June 1952. Like the Lincoln, it was a piston-engine aircraft, and while it did have the range to reach the Soviet Union from British bases, it was not nuclear-capable. The RAF planned to use them against Soviet bomber bases. The Washingtons suffered from maintenance problems due to a lack of spare parts, and most were returned to the US between July 1953 and July 1954; four remained in service until 1958. Their role was assumed by the new jet-propelled English Electric Canberra bomber. In service First generation When the first Blue Danube atomic bombs were delivered to the Bomber Command Armaments School at RAF Wittering on 7 and 11 November 1953, the RAF had no bombers capable of carrying them. Sir William Penney noted that "the RAF has handled aircraft for a long time and can fly Valiants as soon as they come off the production line. But the Royal Air Force has not yet handled atomic weapons, therefore, we must get some bombs to the RAF at the earliest possible moment, so that the handling and servicing can be practised and fully worked out." The Canberra and Valiant were accorded "super priority" status on 13 March 1952, and in December the Vulcan and Victor also received it. The Valiant went into production as the first V bomber in 1955. The Valiant entered service in February 1955, the Vulcan in May 1956 and the Victor in November 1957. No. 232 Operational Conversion Unit was formed at RAF Gaydon in June 1955 and aircrew training commenced. The first Valiant squadron, No. 138 Squadron, formed at RAF Gaydon in January 1955, followed by No. 543 Squadron, which was formed at RAF Gaydon on 1 June 1955 before moving to RAF Wyton. Two more Valiant bases were established at RAF Marham and RAF Honington in 1956, and six more squadrons were formed in quick succession: No. 214 Squadron at RAF Marham in March, No. 207 Squadron at RAF Marham and No. 49 Squadron