In October 1958 BOAC operated the first transatlantic jet service with the larger and longer-range Comet 4. In the 1950s turbine powered airliners were developing rapidly, and the Comet and the seriously delayed Bristol Britannia were soon rendered obsolescent by the flight of the swept-wing Boeing 367–80 (707 prototype) in 1954. In 1953 Vickers had started building the swept wing VC-7/V-1000 with Rolls-Royce Conway turbofan engines, but BOAC short-sightedly decided the Britannia and Comet 4 would be adequate for its purposes, and when the military version of the V-1000 was cancelled in 1955 the 75% complete prototype was scrapped. In October 1956 BOAC ordered 15 Boeing 707s with Conway engines (briefly the most economical commercial engine option). They entered service in 1960. (The British airworthiness authorities insisted on tail-fin modifications which Boeing made available to all 707 users.) Sir Giles Guthrie, who took charge of BOAC in 1964, preferred Boeing aircraft for economic reasons, and indeed BOAC began turning a profit in the late 1960s. After a row in Parliament the government instructed BOAC to purchase 17 Vickers VC10 aircraft from a 30-aircraft order which Guthrie had cancelled. The Standard VC10 had higher operating costs than the 707, largely due to BOAC's requirement at the design stage for the aircraft to have excellent hot and high performance for Commonwealth (African/Asian) routes, but the larger Super VC10 was a success with American passengers on the North Atlantic and was profitable. The next major order of Boeing aircraft was for 11 747-100s. On 22 April 1970 BOAC received its first 747, but the aircraft did not enter commercial service until 14 April 1971 due to BOAC's inability to settle crewing and pay rates with the British Air Line Pilots' Association. BOAC's successor British Airways later became the largest Boeing customer outside North America. The first attempt at a merger of BOAC with BEA arose in 1953 out of inconclusive attempts between the two airlines to negotiate air rights through the British colony of Cyprus. The Chairman of BOAC, Miles Thomas, was in favour of the idea as a potential solution to a disagreement between the two airlines as to which should serve the increasingly important oil regions of the Middle East, and he had backing for his proposal from the Chancellor of the Exchequer at the time, Rab Butler. However, opposition from the Treasury blocked the idea, and an agreement was reached instead to allow BEA to serve Ankara in Turkey, and in return to leave all routes east and south of Cyprus to BOAC.