The same "compound helicopter" concept was used on the Lockeheed AH-56 Cheyenne helicopter of the 1960's. The Cheyenne used the same rigid-rotor and pusher propeller technology. The compound concept was an attempt to create a faster helicopter. Unfortunately, the Cheyenne was cancelled in 1972 because of a couple of accidents related to the rigid rotor and because the USAF A-10 Thunderbolt II (Warthog) and USMC AV-8B Harrier were authorized. the Army went on to change their specification and sacraficed speed in favor of survivability, resulting in the AH-64 Apache.
http://en.wikipedia.org/wiki/AH-56_Cheyenne
