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 in a bunker beneath Hangar 51.
In 1957, Indiana Jones and Antonin Dovchenko discovered the rocket sled of Hangar 51 during their brawl when they cracked and fell through a glass window in the floor. When Dovchenko accidentally engaged the sled's engine after getting knocked into the control panel, the pair were carried down the track, burning five Soviets during the ignition and reaching speeds so high that Dovchenko lost consciousness. Once out of the hangar, Jones shoved the unconscious Soviet aside but, disoriented from the ride, lost his balance and fell to the ground, avoiding being 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). 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 watch 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)