NASA's Hypersonic North American X15 aircraft: On 3 October 1967, Maj. William Knight set a speed record of Mach 6.72 or 4,520 mph (over 6 times the speed of sound) in this aircraft.
For take-off, X15 was attached under the wing of a B-52 (8 engined Heavy lift transport aircraft) and dropped at desired altitude. After flight, It landed on its own like a normal fighter aircraft.
This is the only human controlled aircraft built so far that is propelled by a rocket engine XLR11. Development of this engine had begun way back in 1944.
FUEL: Ethyl alcohol and liquid oxygen. It produced 1500 lbf (6.7 kN) of thrust from four combustion chambers.
The engine was not throttleable but each chamber could be turned on and off individually, thereby reducing or increasing power.
Early flights used two XLR11 rocket engines, but later flights were undertaken with a single engine generating 57,000 pounds (250 kN) of thrust. The XLR99 could be throttled, and were the first such controllable engines for X15.