Royal Naval Museum


The Enigma Machine

One of the most prized artefacts in the Royal Naval Museum artefacts collection is an M4 four rotor German Enigma Machine. During the Second World War, the Enigma cipher system was one of the most complex code systems ever devised and breaking it was of vital importance to the outcome of the Battle of the Atlantic.

The Enigma machine was first patented in 1919 for use by the Post Office and railways. It consisted of a standard keyboard with 26 letters but no numerals or punctuation symbols. Behind the keyboard, a lampboard with 26 small windows marked with the letters of the alphabet, would light up one at a time when a key on the keyboard was pressed. A scrambler unit consisting of three rotating drums (later four) behind the lampboard, scrambled the message which would only repeat itself after 16,900 keyings.

The enigma machine at the RNM

A secret code-breaking base was established at Bletchley Park near Milton Keynes to counter and break the Enigma code. An electro-mechanical device known as Bombe (forerunner of the computer), was built which could calculate hundreds of computations every minute. In May 1941, the first major breakthrough occured when HMS Bulldog captured the German U-boat U110 and a party was able to capture an Enigma machine intact, which enabled code breakers to alert convoys of U-boat positions. A fourth rotor added to the Enigma machine by the Germans in 1942 again baffled code-breakers until U559 was captured by HMS Petard and code books taken before the U-boat sank. By early 1943, the number of British vessels sunk by U-boats had halved.

The Enigma machine in the Museum's collection was made by Olympia Buromaschinewerke of Erfut. It was used by Kommando der Marine Station Der 021, Norwegian Harbour Police and was donated in 1983 by the Royal Naval signal school at HMS Mercury.

The Enigma machine can be viewed in the Lewin Gallery of the Royal Naval Museum. For more information about the machine see our information sheet.

Choice of Richard Noyce Curator of Artefacts

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