The President

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... From the home of the codebreakers and the birthplace of modern computing, this is the Bletchley Park podcast.

Welcome to the October 2025 episode of the Bletchley Park podcast, the SIS at BP.

Today, GCHQ is an independent British intelligence organisation.

However, during World War II, GCSNCS, as it was then called,

continued to be subordinate to the British Secret Intelligence Service, known as SIS or MI6.

The chief of SIS was also the director of GCCS. In this episode, we explore the relationship

between those two organisations,

the part that SIS played in supporting GCNCS and the ongoing presence of SIS at Bletchley Park itself.

We are joined as usual by our research historian, Dr David Kenyon, and by a special guest,

historian and expert in the wartime SIS, Dr. Claire Hubbard Hall.

David, let's start with you. How did GCNCS, the government code and cipher school, come about?

And can you tell us about its relationship with SIS? GCNCS, the government code and cipher school, come about? And can you tell us about its relationship with SIS?

GCNCS, as many of our regular listeners will know, is actually formed in 1919 by the amalgamation

of the two service code-breaking organisations which have existed in World War I, which is

MI1B in the Army and NID 25, better known as

Room 40, in the Navy, in the Admiralty. And what happened at the end of the war was initially

there was a suggestion that nobody needed to do code breaking anymore. This kind of happens in

1946 as well, but they get over themselves. But the plan was that it should

be scaled down, obviously, because there was no war, and made into a civilian organization.

So GCNCS, the government code and cipher score that's created. Initially, it's actually run by the

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