SA-4

The major addition to this flight was that, in order to test the rocket's ability to deal with an engine failure during the flight, one of the engines would be programmed to shut down about 100 seconds after launch. If all went well the rocket would reroute the fuel for this engine to the other engines and have the rocket burn longer to compensate for the loss of acceleration. This was used successfully on the later Apollo 6 and Apollo 13 flights (both Saturn V rockets).