In 1959, Lord Douglas said that Boeing and de Havilland Aircraft Company should work together to make trijets. Boeing made the 727 and de Havilland made the D.H.121 Trident. The two planes were quite similar, but the 727 was a bit bigger. Boeing wanted to use Allison AR963 turbofan engines for the 727. The de Havilland plane also used these engines. Boeing and de Havilland sent engineers to look at each other's designs. However, Boeing decided not to work together with de Havilland and changed the engine.