Check-mate system (original) (raw)

The check-mate system was a system of ship identification used by the Allies of World War II. It was used by the Royal Navy when on patrol looking for German auxiliary cruisers and others ships that had been disguised by Axis forces. Under this system, a patrolling warship or aircraft would individually identify a suspect ship via the Admiralty in London; this step became necessary and was introduced after a British ship that had been captured by Germany twice successfully passed off as still being British when challenged in October 1942.