German code breaking during WW2, Part One

WS, Going Postal
A Colossus Mark 2 computer being operated by Wrens Dorothy Du Boisson (left) and Elsie Booker. The slanted control panel on the left was used to set the “pin” (or “cam”) patterns of the Lorenz. The “bedstead” paper tape transport is on the right

One of the things that most people know about WW2 is that Bletchley Park were successfully decrypting German signals , sometimes before the German recipient had the decoded version himself. But if we could do it , is there any reason the Germans couldn’t do the same to us.

This article is based on the US Army Security Agency’s TICOM (Target Intelligence Committee) investigations and PoW interrogations. The report was published on 1st May 1946 in 9 Volumes. All have been declassified since 2009 and are available on the No Such Agency website. The report refers to Ultra in the first few pages and this in 1946 whereas the public were kept in the dark about Ultra until 1974.

As the war drew to a close , the Americans and British decided they needed to check out what the Germans had been up to. They created exploitation teams who would rush to areas that had been overrun to search for documents , machines and people. This was much like the teams looking for scientists , new weapons and even pilfered art works. Although Ultra had delivered a lot of help with what the Germans were planning , they still had no idea how far the Germans had got with decrypting and reading Allied messages.

Just like we had the bombe and Colossus in Bletchley Park , the Germans were also using and developing machines to break codes. We were only really looking at German stuff , they were looking at American , British , French , Russian and even Italian and Japanese messages. They had their work cut out and concentrated more on the lower and medium level traffic rather than the highest level. With this approach they had some success. Very little of the hardware was captured , even the IBM punched card systems they had used.

The TICOM reports were prepared from captured documents and PoW interrogation. The authors got the impression that most of the PoWs cooperated fully but some were a bit reticent. Some wanted to blow their own trumpets , others to minimise their own contributions. It seems they did not capture that many people who had been involved but did have enough of the top people to paint the picture.

One of the riddles to arise is that , until the 1944 plot against Hitler , there was a lot of duplication of effort with multiple teams of cryptanalysts who would surely have been better employed in one large team , such is inter service rivalry and the egos of the bosses.

There were multiple Signals Intelligence organisations within the Reich. The three military branches each had their own , the High Command of the Armed Forces had one , the Foreign Office had one and Goering’s little pet “Research Bureau” was another. There was some coordination between them but as usual , some hated others and wouldn’t deal with them.

One of the German successes that ought to rewrite part of the history of the Battle of the Atlantic was their ability to read something called British Naval Cypher 3. This was the code used by both the US Navy and the Royal Navy to control the convoys crossing the pond. This was being intercepted and read by the Germans from before 1939 up to 1943 when the code was changed. This was the period corresponding to the greatest loss of shipping. This is hardly surprising when they used these intercepts to direct their submarines to intercept the convoys.

WS, Going Postal
The plugboard of an Enigma machine, showing two pairs of letters swapped: S–O and A–J. During World War II, ten plugboard connections were made

Bletchley Park was also reading the German Naval messages but the Germans knew when the convoys were sailing , the size of the convoy and the planned route. In 1943 the Allies stopped using British Naval Cypher 3 and shipping losses went down dramatically. In the usual fog of war , this reduction is usually attributed to our codebreaking and tactics rather than the more reasonable explanation that the Kriegsmarine was no longer privy to the convoy details.

It is a wonder that the spooks on both sides were unable to put two and two together to figure out why sudden changes in fortune happened. Hindsight is 20/20 but surely when something dramatic happens there has to be a reason. On our side we had the dramatic drop in shipping losses after we switched to a different cypher. On the German side we had the switch from 3 wheel to 4 wheel Enigma by their Navy leading to the Allies not smashing up many U-boats for a good six months. In slight mitigation for the Germans , their experts were convinced their Enigma was uncrackable so it had to be something else , another weakness in teutonic logic. On our side it had to be stubbornness or arrogance , perhaps a mix of the two , then again maybe it was a lot of butt covering.

The Germans also had success with the codes used in North Africa and this goes some way to explaining Rommel’s success when he pushed us back to El Alamein.

Before the war the Germans were busy with diplomatic codes and eavesdropping on telephone calls , the second of these was frowned upon by Neville Chamberlain who thought it was something gentlemen ought not to do.

Before the Anschluss with Austria , Adolf knew that the French were not going to stop him because he had the details from decrypted messages to Paris. He marched across the border knowing he was not going to be stopped.

Similarly during Chamberlain’s dramatic Munich visit and negotiations , Adolf knew that the French were prepared to stop him taking Sudetenland but only if we would do the same. Our Neville was not prepared to use force and this both gave the Germans the green light and cheesed the Frogs off immensely. This knowledge was again extracted from intercepted communications. Sometimes Adolf even delayed negotiations by a couple of hours until he had the decrypted messages that had just been sent to Paris or London.

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