The first tests of the X-51A took place back in 2009 year. The bomber was a B-52 bomber. The tests were deemed successful at 95%. The problem was interruptions in communication with a hypersonic device. During its three-minute flight, the rocket was able to accelerate to 5 Mach numbers.
The next few tests failed. However, in 2013, X-51A was able to fly 430 km, reaching speed in Mach 5,1. The flight lasted six minutes. To date, this test is the most successful.
According to the original plans, the hypersonic rocket should have been put into service in the 2017 year, but now the Pentagon states that the X-51A will enter the army no earlier than the 2020 year.