The Western world's most important medium /heavy lift helicopter, the CH-47 is a lineal descendent of the twin rotor Piasecki helicopter of the late 1940s for piasecki became Vertol, which became Boeing CH-47 CHINOOK  Boeing  Vertol and finally Boeing Helicopters. Development of the Chinook began in 1956 and the first prototype flew in September 1961. The CH-47A, B, and C variants performed with great distinction in the Vietnam War, especially for tasks such as moving artillery. The Chinook is still a vital part of the US Army's inventory, and from 1976 large numbers of older CH-47s have been remanufactured as much improved CH-47Ds the first being redelivered in 1982 in a program to complete 436 machine by 1993.