In 1938 the Government purchased a country mansion in Buckinghamshire to house the Government Code and Cypher School in preparation for the expected war. This was Bletchley Park. As the war progressed huts and then blocks were built in the grounds of the mansion to accommodate the ever increasing workforce.

Bletchley Park was an intelligence factory. Messages containing key information about the enemy’s tactics and strategy were deciphered, evaluated and interpreted in different sections to maintain security. It was then vital to collate and collectively analyse information from all sections to produce actionable intelligence that could be used to win the war.

But Bletchley Park was not only about intelligence; it was on the cutting edge of technology. Here, the codebreaking effort was mechanised using pioneering techniques, which enabled codebreaking to take place on an industrial scale. It was at Bletchley Park that the world’s first computer, Colossus, was operative.

Bletchley Park contributed to shortening the Second World War by up to two years, saving an estimated 20 million lives. Here are some examples of why Bletchley Park was so important to the war effort.

Battle of the Atlantic

Attacks by U-Boasts in the Atlantic were causing high shipping losses, which had they continued could have starved Britain into defeat. The breaking of the Naval Enigma enabled Bletchley Park to know where the U-Boats were positioned so that the shipping convoys carrying food and war supplies could avoid them.

Hut 8

Hut 8 where codebreakers worked on the Naval Enigma


The following is an excerpt from an account by Tommy Flowers describing the value of Lorenz decrypts for D-Day:

“On 5 June, Eisenhower was in conference with his staff when a courier arrived from Bletchley Park and handed him a piece of paper to read. Hitler had sent Field Marshall Rommel battle orders by radio transmission, which Bletchley Park had decoded with the aid of the new Colossus. Hitler had told Rommel that the invasion of Normandy was imminent, but that it was a feint to draw troops away from the channel ports, against which the real invasion would be launched later. Rommel was not to move any troops.

He was to await the real invasion, which could be expected five days after the Normandy landing. This was what Eisenhower read from the paper. He then knew that he could start the invasion of Normandy assured of five days without determined opposition-enough time to build up his forces even with indifferent weather. But he could not tell his assembled officers what he had just read. He just handed the paper back to the courier and said, ‘We go tomorrow.’ And on the morrow, 6 June, they went.”

(Flowers, T.H. ‘D-Day at Bletchley Park’ in Copeland, B. J. (Ed) Colossus: The Secrets of Bletchley Park’s Codebreaking Computers, (2006: 80-81) Oxford University Press).

Enigma decrypts also provided supporting information to the D-Day deception in particular the decrypts of the Abwehr Enigma. Breaking the Abwehr Enigma allowed the Allies to analyse the success of a number of operations intended to deceive the Germans.

Some valves on the Colossus rebuild at TNMOC

Some valves on the Colossus rebuild at TNMOC

Battle of Kursk

After their failure at Stalingrad, the Germans planned a major assault on the city of Kursk in an attempt to break through Russian lines. Lorenz decrypts enabled Bletchley Park to warn the Russians of the intended attack including how the attack was planned and what Army groups would be involved.

Battle of Cape Matapan

Breaking of the Italian naval ciphers enabled the British fleet to achieve victory over the Italian fleet at the Battle of Cape Matapan by discovering details of the battle plans.

Paratroop Drop, Normandy

The Allies planned to drop 1,000 paratroops at a point behind the enemy defence lines in Normandy; however, a Lorenz decrypt showed that a German infantry division had been brought up to that area. The men would have been shot as they slowly drifted down in their parachutes. They were later dropped successfully, further down the coast. From mid-1942, Lorenz decrypts gave massive help in the important task of establishing where the enemy units were positioned or Order of Battle.

Lorenz label

Lorenz Badge on a Teleprinter

South Central Italy

Allied troops landed in South Central Italy and had to push the Nazi forces right back up to the North, thus liberating the country. The Testery broke a large number of messages to help in this war effort.

After the War

After the war, the brilliant minds of Bletchley Park went on with their lives, unknown and unrecognised. They were unable to speak of their vital contribution to the war: unable to tell their families, unable to tell their friends. The Enigma secret was kept until the mid-1970s, but Lorenz was kept secret until the late 1990s.

For an overview of Bletchley Park please click here.