Sublight engines, also known as sublight drives sublight thrusters, or sublight jets were engines that let starships break through an atmosphere and fly through realspace at speeds below the speed of light. In order to attain speeds beyond the light threshold, a ship required a hyperdrive. The most common type of sublight drive was the ion engine. While starfighters used small yet powerful drives, capital ships had vast engines the size of entire buildings.
Technically, the term sublight drive could refer to a wide variety of propulsion techniques: light sails, ramjets, even solid chemical booster rockets. Most sublight drives though used a fusion reaction to break down fuel into charged particles, which were then expelled from the ship in order to create thrust. Because of the heat and mild radioactivity of this thrust, it was illegal to use in or near the atmosphere of most inhabited worlds, though some individuals were not above breaking these laws in order to make a quick getaway.
Sublight engines could accelerate a starship at many thousands of times standard gravity, allowing it to get clear of a planet's gravitational field in a matter of minutes and cross vast distances of realspace. In order to protect its occupants from being killed by the tremendous G-forces involved, starships were equipped with acceleration compensators.