SpaceX Experiments with Restarting Engines on First Stage Descent

Spacex shows pictures of the re-ignition of the rocket engine over the ocean which was a step towards reusable rockets
NextBigFuture, 17 October 2013
http://nextbigfuture.com/2013/10/spacex-shows-pictures-of-re-ignition-of.html

Though not a primary mission objective, SpaceX was also able to initiate two engine relights on the first stage. For the first restart burn, we lit three engines to do a supersonic retro propulsion, which we believe may be the first attempt by any rocket stage. The first restart burn was completed well and enabled the stage to survive reentering the atmosphere in a controlled fashion.