The Boeing-Vertol CH-47 Chinook is among the heaviest lifting Western helicopters. It was originally designed by Vertol in 1957 for the US Army to replace the piston engine-powered Sikorsky CH-37 Mojave. The CH-47 Chinook served extensively in Vietnam. The CH-47D entered service in 1982 with improvements which included upgraded engines, composite rotor blades, a redesigned cockpit to reduce pilot workload, and advanced flight control system.