The Codebreakers of Room 40

The Codebreakers of Room 40

The Room 40 Codebreakers

In 1914, war was declared between England and Germany…a war that would soon cover the world. But this war was unlike any of the wars before it. Technology had advanced far and quickly in the decade prior, and the nations soon found that new methods of warfare were available to them–and not just on the battlefield. Changes had come that would change the landscape of intelligence-gathering forever too.

A New Intelligence in the Great War

One of the first actions of the Great War was to cut the Trans-Atlantic cable that had been connecting Europe to North America. England knew that if they cut the cable, it would greatly hinder Germany from communicating with and recruiting aid across the sea. Of course, telegrams now had wireless technology available to them…and a curious thing was soon discovered.

New technology in England allowed them to snatch those wireless communications right out of the air.

The discovery was accidental–but the implications were HUGE. It was reported to the Navy, and soon they’d scrabbled together a team to investigate and to put this windfall to use. They were quite literally able to intercept every…single…telegram coming from the Continent, because England was the relay point. That meant ALL German communications. But of course, the Germans weren’t just sending out plain text. They were sending their telegrams in code.

Enter the Codebreakers.

An initial team of gentlemen were brought in who had a knack with breaking codes. Dilly Knox, his brother Alfred, William Montgomery, Nigel de Grey…some of them were mathematicians. Some were linguists. Some where history professors. Bankers. Music critics. They were reruited because they had a “something.” A knack. A skill. But what to do with them?

The British Admiralty didn’t know, at first. They knew they could be useful, but they had no place for such an unprecedented team. They assigned them, first, a closet connected to the director’s office. But their very existence was top secret, so every time a visitor came in, they had to scramble to hide.


Soon the Admiralty granted they needed a room of their own, so they assigned them an office. Old Building, Room 40. It was often referred to as OB40 or Room 40.

How Did They Crack the Codes?

The Germans and their allies were employing many different kinds of codes and cyphers, and the Codebreakers had to determine which ones were being used in each message intercepted, and then sort out how to crack them.

Most of their work was accomplished very logically: they captured the codebooks from downed aircraft and sunken U-boats. Once the books were in hand, it was a simple but laborious process of applying the code to each message…before the next day’s variant was employed. A new variant was set at midnight each night, and the codebreakers on the night shift would be expected to work out the new key by the time the day shift arrived or face unending teasing.

But sometimes they weren’t codes–they were cyphers. These didn’t have a handy key that would help if they could get their hands on the book, they required actual cracking. The Codebreakers of Room 40 had to crack cyphers many times over the course of the war as well.

What Happened with the Information?

But though the Room 40 codebreakers were soon churning out decrypted communications daily…what then? The Admiralty, quite frankly, didn’t trust the information at first. It was outside their experience, and the civilian codebreakers had no idea about military protocol, to put the information into terms that would make sense to the military. For quite a while, they were constantly butting heads and frustrating each other. Eventually, a new director was named–Reginald “Blinker” Hall–and he soon assigned a liaison to take the raw data the codebreakers provided and turn it into information that the military knew what to do with.

Even so, they soon discovered a new conundrum: they couldn’t act on much of the information without revealing their hand. If Germany knew they were intercepting communications, they would take actions to stop them, and then they’d lose it all. So before anything could be used, they first had to find another excuse for how they came by the information.

Did Room 40 Grow?

By the end of the war, Room 40 had grown to occupy an entire floor of the Old Building. They had dozens of codebreakers on staff and scores of secretaries–but no “tea girls,” like the rest of the Admiralty, because secrecy was still their byword. Every single person employed in the division was directly recruited by an existing member, so that absolutely everyone was trusted. They had parties, wrote bad poetry about themselves, sang songs, and became a family in many ways.

What’s more, by the end of the war, the Admiralty not only recognized their superb work as having been critical to the war effort, they were in fact largely responsible for the end of the war; they “leaked” a doctored photograph to Germany that showed the Navy in mutiny, which so disheartened the German troops that they insisted upon an armistice.

What Happened Afterward?

After the Great War, most of the employees of Room 40 went back to their ordinary lives…but not all. Quite a few were recruited for a new endeavor: a school dedicated to training up the next generation of cryptographers.

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