In 1960, Boeing bought Vertol Aircraft Co., a helicopter manufacturer in Philadelphia, Pa. The company had three tandem-rotor helicopters under production: the Chinook for the Army, the Sea Knight for the Navy and the Marines, and the commercial 107-11 for the airlines. After the Vietnam War, Boeing and the Army began development of the CH-47D. The CH-47D featured composite rotor blades, an improved electrical system, modularized hydraulics, triple cargo hooks, avionics and communication improvements, and more powerful engines that can handle a 25,000-pound useful load, nearly twice the Chinook's original lift capacity. To extend the service life of the CH-47 beyond 2030, Boeing developed the CH-47F in the mid-1990s and began production in 2003.