Key point: You don't become the world's most dominant military without taking risks.
Weapons die for all kinds of different reasons. Sometimes they happen at the wrong time, either in the midst of defense austerity, or with the wrong constellation of personnel. Sometimes they fall victim to the byzantine bureaucracy of the Pentagon, or to turf fights between the services. And sometimes they die because they were a bad idea in the first place. For the same reasons, bad defense systems can often survive the most inept management if they fill a particular niche well enough.
This article concentrates on five systems that died, but that might have had transformative effects if they had survived. These transformations would only rarely have changed the course of wars (countries win and lose wars for many reasons besides technology), but rather would have had ripple effects across the entire defense industrial base, altering how our military organizations approached warfighting and procurement. Not all the changes would have been for the best; sometimes programs are canceled for sound reasons.
In the early 1960s, the Army was just beginning to appreciate the value of helicopter aviation. The Army had used helicopters at the end of World War II, and used them extensively in Korea for reconnaissance and evacuation purposes. As the sophistication of the machines grew, however, the Army began to see the prospect for much more advanced helicopters that could conduct a wide variety of missions.
The star of the show was supposed to be the AH-56 Cheyenne, a radical design that combined high speed with punching power. The Cheyenne could escort other helicopters in transport mission, or conduct ground support and attack ops independently. In particular, it contained a magnificent propulsion system that could offer speeds of up to 275 miles per hour.