During the 1960s, Lockheed began development for two large aircraft: the C-5 Galaxy military transport and the L-1011 TriStar wide-body civil airliner. Both projects encountered delays and cost overruns. The C-5 was built to vague initial requirements and suffered from structural weaknesses, which Lockheed was forced to correct at its own expense. The TriStar competed for the same market as the McDonnell Douglas DC-10; delays in Rolls-Royce engine development caused the TriStar to fall behind the DC-10. The C-5 and L-1011 projects, the canceled U.S. Army AH-56 Cheyenne helicopter program, and embroiled shipbuilding contracts caused Lockheed to lose large sums of money during the 1970s.