Frigate Bird was the only US test of an operational ballistic missile with a live warhead. This test involved firing a Polaris A1 missile from a ballistic missile submarine. The missile was launched by the USS Ethan Allen (SSBN-608) at 13:18 (local) from a position 1500 nm east-northeast of Christmas Island. The re-entry vehicle (RV) and warhead flew 1020 nm downrange toward Christmas Island before re-entering the atmosphere 12.5 minutes later, and detonating in an airburst at 3352 meters. The system tested was a combination of a Polaris A1 SLBM, and a W-47Y1 warhead in a Mk-1 RV. The Mk-1 RV had a beryllium heat-sink heat shield, and with the 325kg warhead had a gross weight of 408kg. The missile/RV demonstrated an accuracy on the order of 2011 meters.