The Air Force also wanted the plane to have only four engines. This meant that new engines had to be made. On May 18, 1964, Boeing, Douglas, General Dynamics, Lockheed and Martin Marietta designed a plane. General Electric, Curtiss-Wright and Pratt & Whitney designed the engines. The Air Force liked Boeing, Douglas and Lockheed's designs. They also liked General Electric and Pratt & Whitney's engine designs.