Scramjet
Scramjets are a hybrid propulsion system used for vehicles which need to be able to operate in both atmosphere and vacuum. Engines of this type are technically Air-augmented Rockets, since they use a conventional rocket motor to create supersonic airflow through the engine. While true scramjets require the vehicle to already be travelling at hypersonic speeds before they can light, Air-augmented rockets can provide thrust regardless of how fast the vehicle is moving.
While operating in a vacuum, the rocket motor operates by itself. When in an atmosphere, however, the rocket motor additionally causes the compressed air being drawn through the engine to become superheated and expand, dramatically increasing thrust. Scramjet vehicles can operate out of normal airfields and reach orbit unassisted, and many have VTOL capability.
Almost all atmospheric shuttles and military dropships, both GEO and Incorporate, are Scramjet powered. There is very little variation in performance between military and civilian scramjet vehicles, since achieving orbit requires enough speed that further increasing engine power is generally counterproductive.