The BBC has reported that a pair of Enigma machines used in the Spanish Civil War have been given to the head of GCHQ, Britain’s communications intelligence agency. Apparently these machines are two of “around two dozen” discovered “a few years ago, in a secret room at the Spanish Ministry of Defence in Madrid.” The article explains how these “fill in a missing chapter in the history of British code-breaking”. Apparently the use of commercial Enigma machines between Spain and Germany during the Spanish Civil War gave British codebreakers access to live traffic, since military signals used within Germany were too weak to hear in Britain. Within six or seven months, in April 1937, Dilly Knox produced his first decryption of an Enigma message.
As to how this relates to the better known Enigma story, the article explains that:
The machines used in Spain were modified versions of the commercial Enigma machine. The military machine that would be used by Germany during World War II was an order of magnitude more secure because a plugboard was attached to the front.
These more complex signals are where the better known Polish/Bletchley Park story of Enigma fits into the story.
The BBC explains the trade made for the two Enigma machines:
In return the UK handed over a number of items including a German four rotor Naval Enigma machine recovered from Flensburg in May 1945, an Enigma rotor box and related documents. The idea is that this could serve as the foundation of a display on code-making and code-breaking at the Spanish Army Museum
One machine will be held at GCHQ and the other will be placed on public display at Bletchley Park. The full article gives some interesting insight from the GCHQ historian and the director of Spain’s intelligence service.
Source: BBC News – The Spanish link in cracking the Enigma code.