The rocket sled was a high speed sled mounted on a set of rails. A rocket in the back propelled the sled forward. Sleds of this sort were used by the United States of America in the Cold War against the Union of Soviet Socialist Republics to test ejection seats and other equipment for aircrafts. One was stored at a bunker underneath Hangar 51.
In 1957, Indiana Jones discovered the rocket sled of Hangar 51 by, where he fought Antonin Dovchenko, who along with him crushed the glass dome which led them there. When Dovchenko accidentally engaged the sled's engine by getting knocked into the control panel, the pair took off down the track, burning five Soviets and reaching speeds so high that Dovchenko lost consciousness though Jones didn't. Once out of Hangar 51, Jones pushed the unconscious Soviet aside but lost his balance and fell into the sandground dizzy, avoiding getting spotted by Dovchenko once he recovered conciousness and allowing him to escape to Doom Town.
Behind the scenes
In Indiana Jones and the Kingdom of the Crystal Skull, it can be clearly seen that the engine on the sled has compressor blades, indicating a jet engine rather than a rocket motor, so the strictly speaking it's a 'jet sled'.
In LEGO Indiana Jones 2: The Adventure Continues, the rocket sled gets destroyed. Boarded by Jones and the Janitor, with Dovchenko dragged behind from his chain, it leaves the bunker at full speed (without burning any Soviet) and after knocking Dovchenko away from its rails, it crashes against the rubber bumper and sends Jones and the Janitor into Doom Town only to then destroy the bumper and fly into the sky, where it explodes into smithereens. Four prairie dogs then see how its remains fall near their holes.
- Indiana Jones and the Kingdom of the Crystal Skull (First appearance)
- LEGO Indiana Jones 2: The Adventure Continues (Non-canonical appearance)