In addition to NASA’s Hyper-X program (which I mentioned here), there is some other noteworthy scramjet research going on. The Army is interested, too.
Compared to unpowered kinetic energy tank rounds that slow down and lose penetrating power to aerodynamic drag, a scramjet powered round could sustain its tank-penetrating power over longer ranges, or enable a smaller, lighter gun to achieve the same result.
Laboratory flight tests of a 101 mm demonstrator engine, scheduled from April to July of this year, may lead to a live-fire demonstration of a 120 mm round in a tank gun by 2005. Army researchers believe a scramjet-powered kinetic energy penetrating round will help give lighter fighting platforms an improved large caliber, direct fire capability.
With no moving parts, the scramjet engine burns fuel with the compressed, superheated air encountered at Mach 5–the muzzle velocity of existing tank guns.
Timing fuel combustion to the desired flight profile makes it possible to sustain the kinetic energy and penetrating power of tank rounds at extended ranges in direct-fire applications. Alternatively, the scramjet could extend the range of cannon rounds for indirect fires.
I can see it now: The Army will line up ten T-72 tanks side-by-side and an M-1 will shoot a single scramjet penetrator round though all of them. Then Evel Knievel will jump them on a motorcycle.