The Boeing X-37 counts itself among some of NASA's most extreme aircraft. In addition, it's part of the U.S. Space Force, which is a branch of the military. This makes the Boeing X-37, also known as the Orbital Test Vehicle, technically the fastest U.S. military aircraft.

The fact is, most of what the X-37 does is top secret, although the Iranian Government called it a "secret space warplane" The Register reports. Thanks to the Rocketdyne engine, this thing can easily hit Mach 25 according to NASA.

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