MARK STRONG: Bletchley Park was an incredibly secret code breaking facility during the war. The Germans, at the time, had the Enigma machine which was a random generator of letters with which words were made and codes were sent and it was virtually uncrackable.

ALAN TURING: It's beautiful.

MATTHEW BEARD: Essentially the government collected these very eccentric people all under one roof. And I always think of this as sort of an odd bunch of superheroes who all have these very special powers, but wear tank tops and tweed.

SPEAKER 1: They recruited chess champions. They recruited mathematicians-- people who had a willingness to dig into puzzles.

SPEAKER 2: They say they could and now we shall find out, won't we.

MATTHEW GOODE: They were asked to come in. They worked incredible hours. They practically lived at Bletchley.

BENEDICT CUMBERBATCH: They kept their spirits up. There was an incredible collegiate atmosphere that I think it was a very fun, exciting, dare I say it, sexy sort of place to work because they really were spearheading the intelligence needed to win the war.

MARIA DJURKOVIC: All the code breakers-- very young people-- brought to this place and they expanded hugely.

IAIN STANDEN: This place when from being a cottage industry to industrial code breaking factory. From 200 or people at the start of the war to about 9,000 on the books. They were working in huts, which were glorified garden sheds.

KEIRA KNIGHTLEY: These are certainly some of the people that helped win the Second World War and nobody knew about them.

MORTEN TYLDUM: It's one of the best kept secrets in the history of intelligence.

STEWART MENZIES: If you speak a word of what I'm about to show you, you will be executed for high treason.

TEDDY SCHWARZMAN: By all accounts the work that they did at Bletchley shortened the duration of the war by up to two years.

SPEAKER 3: Stalingrad, the Ardennes, the invasion of Normandy. All victories that would not have been possible without the intelligence that we supplied.

BENEDICT CUMBERBATCH: The Nazi's were the bad guys and they were the good guys. It was that simple. And anything to bring about a victory was what they were after.

KEIRA KNIGHTLEY: It shouldn't be forgotten how extraordinary these people were and what they did. I think it's very important that we remember that.

JOAN CLARKE: T.

ALAN TURING: T.

JOAN CLARKE: R.

ALAN TURING: R.

JOAN CLARKE: O.

ALAN TURING: O. T.

JOAN CLARKE: T. A.

ALAN TURING: A.

JOAN CLARKE: H.

ALAN TURING: H.

JOAN CLARKE: Q.

ALAN TURING: Q.

Q.