Here is why the Cheyenne failed to replace the Cobra
The AH-64 Apache has become a legendary helicopter — proving to be more than a capable replacement for the AH-1 Cobras in United States Army service, but this gunship almost didn't see the light of day.
The Apache racked up 240 hours of combat during Operation Just Cause. (Photo from U.S. Army)
Back in the late 1960s, the Cobra was seen as just a stopgap. The Army ran a competition for an Advanced Aerial Fire Support System and, ultimately, selected Lockheed's entry, designating it the AH-56 Cheyenne and ordering ten prototypes.
Cobra AH-1 attack helicopters were often deployed with Loaches to provide greater firepower. (Photo from U.S. Army)
The Cheyenne was not a conventional helicopter. It had a top rotor and a tail rotor, but it also added a pusher propeller. This gave it a top speed of 245 miles per hour, according to MilitaryFactory.com. By comparison, the AH-64 has a top speed of just under 189 miles per hour. The Cheyenne had a single 30mm cannon and could carry BGM-71 TOW missiles, 2.75-inch rockets, and external fuel tanks.
AH-56 Cheyenne hovering over a helipad. (Photo from U.S. Army)
So, why didn't the Cheyenne become a staple? First, a fatal crash and numerous delays marred the project. Additionally, the Army's Cheyenne was seen as a violation of the Key West Agreement, causing further friction. Plans to buy 600 Cheyennes were quickly scaled down to 375 as costs climbed.
Ultimately, the Army scrapped the Cheyenne when the Air Force began the A-X project, which eventually lead to fielding the A-10 Thunderbolt II close-air support plane. The Cheyenne was officially cancelled on August 9th, 1972. Eight days later, the Army began the Advanced Attack Helicopter program, which eventually produced the AH-64 Apache.
An A-10C Thunderbolt II assigned to the 75th Fighter Squadron performs a low-angle strafe using its 30mm GAU-8 rotary cannon during the Hawgsmoke competition at Barry M. Goldwater Range, Ariz., June 2, 2016. The entire A-10 platform was designed around the tank-killing cannon. (U.S. Air Force photo by Senior Airman Chris Drzazgowski)
The Cheyenne hasn't failed entirely, though. Sikorsky's S-97 Raider prototype looks like a more advanced version of the Cheyenne. In a real sense, the Cheyenne was almost five decades ahead of its time.