The U.S. Army has cancelled a controversial planned $39 billion program for a new stealth helicopter called the Comanche.

The decision to scrap the Comanche follows years of study and close to seven billion dollars in development costs.

Instead of the 120 Comanches that would have been purchased over the next five years, the Army is instead proposing to use the money earmarked for that project to buy 800 new aircraft, including more Apache and Blackhawk helicopters as well as unmanned drones.

Army Chief of Staff General Peter Schoomaker acknowledges it was a difficult decision but says it was the correct one.

"It's a big decision," he said. "We know it's a big decision but it's the right decision."

The Comanche was often described as the future of Army aviation.

But officials say a new study drawing on Army experiences in the wars in Afghanistan and Iraq showed the money could be better spent to upgrade and expand the existing fleet of helicopters.

The Pentagon estimates it will cost as much as $680 million to cancel the program.

It is the second major Army weapons system to be scrapped in recent years. A controversial new artillery piece called the Crusader was killed previously.