"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.
The first in the long line of Chinooks was the YHC-1B tandem-rotor transport helicopter that rolled out in 1961. Chinooks first were used in combat in 1965 during the Vietnam conflict. By 1968, the Chinook had put in 161,000 hours of flying time, carrying 22.4 million passengers and more than 1.3 million tons of cargo.
U.S. Army Special Operations Forces operate Special Operations Chinooks, designated MH-47Ds and MH-47Es, among the most advanced rotorcraft in operation today.