WASHINGTON â€"  The Pentagon has finally released a report about what went wrong when its Hypersonic Technology Vehicle (HTV-2) failed just minutes into a test flight last year and barreled into the Pacific Ocean.

The unmanned, arrowhead-shaped aircraft, which one day could allow the US to strike anywhere across the globe in less than 60 minutes, was strapped to a rocket and launched from California's Vandenberg Air Force Base last August.

The drone coasted at speeds of 13,000mph (21,000kmph) -- 20 times the speed of sound -- through the Earth's atmosphere for less than three minutes before ultimately failing and switching into abort-mode just nine minutes into the flight. It splashed down short of its intended target near the Kwajalein Atoll in the Pacific.

Defense Advanced Research Projects Agency (DARPA) said an analysis of the crash showed that high speeds peeled off larger-than-expected portions of the vehicle's skin.

'HTV-2's first flight test corrected our models regarding aerodynamic design.'

- Air Force Maj. Chris Schulz

Officials anticipated some of the outer shell would gradually wear away, but rapidly-forming gaps on the skin created strong shock waves around the HTV-2 and caused it to roll abruptly, the report said.

Military researchers, however, were hopeful that they could learn from the mistakes of the failed flight, especially after the first HTV-2 mission in April 2010 -- which also terminated early -- prompted successful adjustments to the craft's aerodynamic design.

"HTV-2's first flight test corrected our models regarding aerodynamic design within this flight regime," Air Force Maj. Chris Schulz, DARPA program manager, said in a statement. "We applied that data in flight test two, which ultimately led to stable aerodynamically controlled flight."

Schulz added that data collected during the second test flight "revealed new knowledge about thermal-protective material properties and uncertainties" for flights at such a high speed in our atmosphere. Going forward, that data will be used to modify how the vehicle's outer shell responds to heat stress, DARPA said.