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A "revolution in aviation" may finally be underway. For years the supersonic combustible ramjet has been theorized. And in the last year or so several actual test flights have taken place in various countries.

NASA recently had a successful test flight of the X-43A. "It flew for 10 seconds on its own power over California, then glided for six minutes before falling into the ocean." The X-43A flew at mach 7, and NEW speed record (breaking the previous x-15 mark of 6.7 set in the 60s). Its not quite a total reality yet, but its a step towards a real scramjet.

The scramjet engine is of monumental significance because it has no moving parts and does not require onboard oxygen to be used to combust the hydrogen fuel, as a rocket engine does. This is an enormous advantage (for example the Shuttle requires 143,000 gallons of liquid oxygen, which weighs 1,359,000 pounds).

Instead of carrying onboard oxygen the scramjet gets it from the atmosphere by forcing the atmospheric air into the combustion chamber at supersonic speeds. There the oxygen is mixed with hydrogen and combusted. Combustion only works at supersonic speeds because such speeds are required to compress the air. Then the result of the combustion is exhaust gas that provides thrust.

See the links for more info.   Nasa jet smashes speed record