On 21 March 2007 two crew members of the Royal Navy's Trafalgar-class submarine, HMS Tireless were killed in an explosion caused by air-purification equipment in the forward section of the submarine. The submarine was in service in the Arctic Ocean and had to make an emergency surface through the pack ice. A third crewmember who suffered "non-life-threatening" injuries was airlifted to a military hospital at Elmendorf Air Force Base near Anchorage, Alaska.