Check-mate system facts for kids

The check-mate system was a clever way for the Allied forces to tell friendly ships apart from enemy ships during World War II. The Royal Navy, which is Britain's navy, used this system a lot. They were looking for German warships that were disguised as regular cargo ships.

This system became super important after a British ship, which had been captured by Germany, tricked Allied patrols twice in October 1942. With check-mate, a patrolling warship or aircraft would check with the Admiralty in London to identify any suspicious ship.

The German auxiliary cruiser Atlantis was a warship disguised as a normal cargo ship. It pretended to be different ships like the Norwegian MV Tamesis to trick Allied patrols.

Why the System Was Needed

During the war, German warships, called auxiliary cruisers, sailed across the Atlantic and Indian Oceans. Their main goal was to find and attack Allied cargo ships. These German warships often looked like regular merchant ships to avoid being caught.

Enemy cargo ships that were already at sea when the war started helped these German warships. They would give them fuel and supplies. If the Germans captured an Allied cargo ship, they could also use it to resupply their own ships. All these enemy ships would pretend to be neutral or Allied cargo ships if they met an Allied patrol.

Before the check-mate system, Allied warships had lists of friendly ships they expected to see. These lists were updated by radio. But often, Allied warships would find friendly ships that were not on their lists. Also, many British ships did not use the correct secret code when challenged. Foreign ships were even worse at responding correctly. The lists also sometimes had misspelled names or old names of ships that had been renamed. This made it very hard to know who was who.

How Check-Mate Worked

The check-mate system started working fully on June 8, 1943. From that day on, the Allies estimated where every ocean-going cargo ship in the world was each day.

When an Allied patrol aircraft or warship saw a new ship, they had to identify it. They used a special code for the ship's description and a register of ship shapes. They compared these to their list of expected ships and a secret signal.

If they were not sure about a ship's identity, the Allied patrol could send a simple radio message to shore. They would usually get a reply within a few minutes. The message they sent looked like this:

• EMERGENCY CHECK (stranger's code letters) (alleged name) (position - by lettered coordinates)

The replies they could get were:

• MATE TRUE (meaning the identified ship could be at that location)
• MATE FALSE (meaning the identified ship could not be at that location)
• MATE DOUBTFUL (meaning they needed to investigate the ship further)