Five facts you need to know about Bombe machines

Conceived by legendary computer scientist Alan Turing, the Bombe machines changed the course of World War Two, saving millions of lives. Find out everything you need to know about these amazing devices, care of the experts at Bletchley Park.

Enigma machine at Bletchley ParkBletchley Park

1. Why were Bombe machines needed?

Bletchley Park was set up to decode intercepted German messages, some of which had been encrypted using Enigma machines.

Enigma machines typically changed settings every 24 hours.

Every day, there were many billions of possible combinations. Bletchley Park staff worked around the clock to try and break the settings by hand.

This was slow, painstaking work, so Alan Turing designed the Bombe machine to speed up the decryption process by a huge degree.

Perfected by Codebreaker Gordon Welchman, the first Bombes started work in 1940.

Bombe bay with attending Wrens, Eastcote Outstation (1944)Bletchley Park

2. How did the Bombe machines work, and who used them?

The Bombe helped Codebreakers discover part of an Enigma key – the settings of the Enigma machine used to encipher a message. 

Enigma’s rotors and plugboard meant the Germans could use one of many millions of different encryption settings to send their messages. So the Bombe
machines had somehow to help reveal which was being used, and fast.

The electronic Bombe machine had many sets of drums, each set of three matching up to one Enigma's rotors.

This allowed the Bombe Operators at Bletchley Park to quickly check which Enigma settings might have been used to encrypt a message.

Hundreds of Wren (Women's Royal Naval Service) workers were responsible for operating the Bombe machines.

But it was dull and oppressive work - the women worked long shifts in dark, stuffy rooms.

Eastcote OutstationBletchley Park

3. What was the impact of the Bombes?

By speeding up the process of breaking the Enigma's encryption settings, Turing’s invention meant that Bletchley Park staff could decode messages quickly and pass on the intelligence – often with enough time for it to be acted upon.

Intelligence uncovered before the battle of El Alamein in 1942 contributed to victory in this Egyptian campaign, which proved to be a turning point of the war.

Testing Bombe results in the Decoding Room, Hut 6 at Bletchley ParkBletchley Park

4. Which parts of the war did Bombe machines help?

The use of Bombes in intelligence-gathering had a huge impact across many land, sea and air campaigns.

The German battleship Scharnhorst was located using Enigma decrypts (messages encrypted by Enigma and deciphered with help from a Bombe), and sunk in December 1943.

Later, in 1944, Enigma decrypts provided details of German defensive preparations for, and reactions to the D-Day invasion.

Hut 6 at Bletchley Park, working on German army and air force Enigma messagesBletchley Park

5. What was the Bombe's legacy?

Bombes represented the first mass-production of a specially designed cryptanalytical machine. They heralded the industrialisation of codebreaking, and the intelligence they provided was crucial to Allied success in WW2. 

The Bombes played a significant role in Bletchley Park's operations.

The secrecy around Bombes and Bletchley Park was so successful that the Germans remained unaware that the information sent on their 'unbreakable' Enigma machines had actually been cracked by the Allies.

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