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The Welcome from the home of the codebreakers and the birthplace of modern computing.

This is the Bletchley Park podcast.

Welcome to the October 22 episode of the Bletchley Park podcast, Shark Attack.

In February 1942, the worst fears of the teams working on naval enigma were realised.

The German Navy introduced a new, more complex enigma machine

for use by its U-boats in the Atlantic. At a stroke, Bletchley Park was no longer able to read messages

sent by the German submarines which were hunting the vital Atlantic convoys. By the end of the year,

however, this new code had been broken, and Bletchley Park was once again able to divine the secrets of the Atlantic U-boats.

But just what was Shark, and how was it broken by the team at Bletchley Park?

In this It Happened Here episode, we're joined by Bletchley Park's research historian, Dr David Kenyon, to find the answers.

Many thanks to Dr Ben Thompson for voicing our archival documents.

Thank you. This is Bletchley Park.

It happened here.

In this episode, we'll be talking about naval enigma.

But before we start, I want to get right back to the basics and ask about what makes naval enigma different.

Is it just the system as used by the Navy or whether different types of enigma machines?

Well, this is a mistake that a lot of people make when people talk about the Enigma machine.

Actually, there's a family of about 20 different machines in the whole evolution of the device. And you don't need to worry about most of them.

When people talk about Enigma, they mostly talk about the I machine, which is the Army and

Air Force machine that was used by the German military during World War II, with three rotors

and a plugboard,

...