COBRA AH-IG
The first U.S. Army helicopter designed to perform attack missions initially flew in 1965. This 1967-built “G” model was modified, then restored to “G” model armament configuration for display. Developed in only 6 months, “Snakes” saw extensive combat in Vietnam beginning in June 1967, and served in all U.S. peace-keeping operations for over 20 years.
For more technical detail, see Wikipedia.