Lockheed L-193 Constellation II

The Lockheed L-193 Constellation II was a jet airliner design concept, drawn up between 1949 and 1953, with a swept wing and engines mounted towards the tail. An airliner and a tanker version were developed, and Lockheed sought requirements from Trans World Airlines for the airliner. The engines were flush mounted to the fuselage, a feature dropped from most later jet designs, and the tail-mounted engine layout was later used by the Lockheed JetStar, the Vickers VC-10 and the Ilyushin Il-62. A modified L-193 won an aerial refuelling competition initiated by the United States Air Force and was chosen in 1955 to supplement the interim KC-135 tanker, and a prototype was ordered in February 1955. The Boeing KC-135 could be delivered two years earlier and enter squadron service four years earlier, it performed well, the L-193 was never ordered as a tanker, and the airliner plans were dropped soon after.