The check-mate system was a system of ship identification used by the

Allies of World War II The Allies, formally referred to as the United Nations from 1942, were an international military coalition formed during the Second World War (1939–1945) to oppose the Axis powers, led by Nazi Germany, Imperial Japan, and Fascist Italy. ...

. It was used by the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

when on patrol looking for

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...

auxiliary cruiser An armed merchantman is a merchant ship equipped with guns, usually for defensive purposes, either by design or after the fact. In the days of sail, piracy and privateers, many merchantmen would be routinely armed, especially those engaging in lo ...

s and others ships that had been disguised by

Axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...

forces. Under this system, a patrolling warship or aircraft would individually identify a suspect ship via the

Admiralty Admiralty most often refers to: *Admiralty, Hong Kong *Admiralty (United Kingdom), military department in command of the Royal Navy from 1707 to 1964 *The rank of admiral *Admiralty law Admiralty can also refer to: Buildings * Admiralty, Traf ...

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. Hilfskreuzer Atlantis

Background

German auxiliary cruisers prowled the Atlantic and Indian Oceans searching for Allied merchant ships. Axis merchant ships overseas when the war began were used to refuel these auxiliary cruisers,

pocket battleship The ''Deutschland'' class was a series of three ''Panzerschiffe'' (armored ships), a form of heavily armed cruiser, built by the ''Reichsmarine'' officially in accordance with restrictions imposed by the Treaty of Versailles. The ships of the cl ...

s, and long-range

U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role ...

s. Any Allied merchant ships captured by German ships could be similarly used for resupply. These Axis-crewed ships pretended to be neutral or Allied merchant ships if they encountered Allied patrols. Before check-mate, Allied warships patrolling for Axis ships were given a list of Allied ships they were likely to see, and the list was periodically updated by radio signals from shore. Through the first half of the war, Allied warships frequently encountered Allied ships not on their lists. Only half of British ships correctly answered a challenge with their secret code, and foreign ships were even less likely to respond appropriately. The lists often contained misspelled names or former names of renamed ships.

Implementation

The check-mate system became fully operational on 8 June 1943. From that date the Allies estimated the daily position of every independently routed ocean-going merchant ship in the world. The check-mate system required the Allied patrol aircraft or warship to identify each newly encountered ship with a Merchant Ship Description Code and a Merchant Ship Silhouette Characteristics Register in comparison to their list of anticipated contacts and the secret signal. If identification was uncertain, the Allied patrol could make a plain language radio query to shore and expect a reply within a few minutes. The query format was: * EMERGENCY CHECK (stranger's

code letters Code letters or ship's call sign (or callsign) Mtide Taurus - IMO 7626853"> SHIPSPOTTING.COM >> Mtide Taurus - IMO 7626853/ref> were a method of identifying ships before the introduction of modern navigation aids and today also. Later, with the i ...

) (alleged name) (position - by lettered coordinates) Possible replies were: * MATE TRUE (the ship could be there), * MATE FALSE (the identified ship could not be at that location), or * MATE DOUBTFUL (requiring further investigation by the patrol)

References

{{DEFAULTSORT:Check-Mate System History of the Royal Navy