The DC-3 resulted from a marathon telephone call from American Airlines CEO C. R. Smith to Donald Douglas, when Smith persuaded a reluctant Douglas to design a sleeper aircraft based on the DC-2 to replace American's Curtiss Condor II biplanes. The DC-2's cabin was wide, too narrow for side-by-side berths. Douglas agreed to go ahead with development only after Smith informed him of American's intention to purchase twenty aircraft. The new aircraft was engineered by a team led by chief engineer Arthur E. Raymond over the next two years, and the prototype DST (Douglas Sleeper Transport) first flew on December 17, 1935 (the 32nd anniversary of the Wright Brothers' flight at Kitty Hawk) with Douglas chief test pilot Carl Cover at the controls. Its cabin was wide, and a version with 21 seats instead of the 14–16 sleeping berths of the DST was given the designation DC-3. There was no prototype DC-3, and the first DC-3 built followed seven DSTs off the production line for delivery to American Airlines.