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ENIGMA'S SECRET TWIN

Most of us know the story of Enigma, the German cipher machine eventually broken by clever people at MI6's country house, Bletchley Park, following brilliant early work by Polish mathematicians. The achievement, reckoned to have shortened the war by two years, remained secret for decades. Also secret, and less well known to this day, was the fact that Britain had Enigma too. That's why the Germans--no slouches at code-breaking--couldn't read British signals.

In the 1920s a German company, Enigma Chiffriermaschinen Aktiengesellschaft (ECA), marketed Enigma and the German government bought and developed it. In 1935, German code-breakers broke the Royal Navy's main cipher, with disgraceful ease, when a naval detachment in Aden during the Abyssinian crisis carelessly used codes that were intended only for wartime.

Given that, I wondered, how did they not learn that the British were reading Enigma in the war? Granted, Enigma intelligence was usually disguised as the product of aerial reconnaissance, direction-finding, MI6 spies or interrogating prisoners, but not all of it could be and basic decrypts often had to be transmitted. What system carried them, what ensured that the Germans never knew what they were monitoring? The answer was a machine called Typex which looks like Enigma's slightly bigger twin. That's because it was Enigma, which Britain had also bought and adapted. The Germans couldn't penetrate their own system.

The story began in 1928 when the Government Code and Cypher School (GC&CS)--forerunner of GCHQ and then part of MI6--acquired two Enigma machines at the Admiralty's request. The Admiralty inexplicably lost interest but in 1934 Wing Commander Lywood of Air Ministry Signals asked the GC&CS if he might borrow one. The correspondence, now in the National Archive at Kew (AIR 2/2720), shows an endearing "Alice in Wonderland" side of British bureaucracy: "You may borrow this machine in order that it may serve as a model for your 'engineers'... I must point out that it is probable that this machine is covered by patents taken out in this country...It may be advisable that you consult your patent experts before proceeding to make a direct copy."

There were three British patents but Lywood began adapting it regardless, with help from GC&CS. Later, Air Ministry Contracts Directorate wrote: "It is suggested that the question of infringement be referred to this branch after the apparatus has been made and used in order that any payment due to the patentee may be considered...no action to settle the matter could be considered while the apparatus is secret."

Effectively, payment to ECA could be considered only after the forthcoming war was won or lost, in which case there would either be no ECA to be paid or no Air Ministry to pay them.

By 1936 the War Office was showing interest in "the RAF Enigma" and the same phrase seems to have been used by a Mr Sidney Hole who wanted to know whether it infringed a patent of his from 1924. The Air Ministry conceded privately: "The machine made for us was copied from the German ‘enigma' with additions and alterations suggested by the GC&CS."

In the best traditions of the bureaucracy it recommended "a suitable non-committal reply" to Mr Hole. In 1937 it admitted to itself that it was infringing patent no. 267472 and concluded, with masterly understatement, that "difficulty arises in remunerating the patentees... since this would entail a suggestion that the Department is using a cypher apparatus similar in some respects to that to which the patent relates."

In other words, we shan't pay what we owe because that would mean admitting to doing that for which we owe. It is not clear what reply Mr Hole received.

Typex was deployed by the RAF and the army at senior levels, often with MI6 operators. MI5 and MI6 used it but the Admiralty did not, until the readability of many of their early wartime signals became tragically apparent. Typex remained secure throughout the war and continued in use afterwards.

It's hard for the cryptographic layman to gauge how far Typex helped to break its sibling. It was clearly useful in replicating Enigma, though someone from GCHQ once told me that the whole story had yet to come out. I've no idea if that's still true but anyone interested could start by looking at Typex in the Bletchley Park museum. And in these litigious times any inheritors of ECA titles or heirs of Mr Hole might even sue for unpaid royalties.

Picture credit: x_jamesmorris (via Flickr) 

(Alan Judd is a novelist and former solider. His latest novel is "Dancing with Eva", Simon & Schuster).