Rockwell International collaborated with the Lawrence National Laboratory in Livermore, CA. for the creation of a scramjet engine for a minimum speed of Mach 8, already reaching Mach 5.5 in 1992.

-Actually it was a small scale test that was launched through some kind of canyon instead of using a test tunnel or an actual supersonic aircraft.

-The cannon used compressed hydrogen to launch the small engine at very high speed.

"Rockwell-Lawrence's Little Scramjet"