Notice of a significant anniversary from the BBC:

Why was the Zimmermann Telegram so important?

By Gordon Corera
Security correspondent

Tuesday marks the 100th anniversary of a remarkable success for British intelligence: but one that involved spying on the United States and then conspiring with its senior officials to manipulate public opinion in America.

On the morning of 17 January 1917, Nigel de Grey walked into his boss’s office in Room 40 of the Admiralty, home of British code-breakers.
It was obvious to Reginald “Blinker” Hall that his subordinate was excited.

“Do you want to bring America into the war?” de Grey asked.

The answer was obvious. Everyone knew that America entering World War One to fight the Germans would help break the stalemate.

“Yes, my boy. Why?” Hall answered.

“I’ve got something here which – well, it’s a rather astonishing message which might do the trick if we could use it,” de Grey said.

The previous day, the German foreign minister, Arthur Zimmermann, had sent a message to the German ambassador to Washington.

The message used a code that had been largely cracked by British code-breakers, the forerunners of those who would later work at Bletchley Park.

Zimmermann had sent instructions to approach the Mexican government with what seems an extraordinary deal: if it was to join any war against America, it would be rewarded with the territories of Arizona, New Mexico and Texas.

“This may be a very big thing, possibly the biggest thing in the war. For the present, not a soul outside this room is to be told anything at all,” Hall said after reading it.

Part of the problem was how the message had been obtained.

German telegraph cables passing through the English Channel had been cut at the start of the War by a British ship.

So Germany often sent its messages in code via neutral countries.

Germany had convinced President Wilson in the US that keeping channels of communication open would help end the War, and so the US agreed to pass on German diplomatic messages from Berlin to its embassy in Washington.

The message – which would become known as the Zimmermann Telegram – had been handed, in code, to the American Embassy in Berlin at 15:00 on Tuesday 16 January.

The American ambassador had queried the content of such a long message and been reassured it related to peace proposals.

By that evening, it was passing through another European country and then London before being relayed to the State Department in Washington.

From there, it would eventually arrive at the German embassy on 19 January to be decoded and then recoded and sent on via a commercial Western Union telegraphic office to Mexico, arriving the same day.

Thanks to their interception capability process, Britain’s code-breakers were reading the message two days before the intended recipients (although they initially could not read all of it).

A coded message about attacking the US was actually passed along US diplomatic channels.

And Britain was spying on the US and its diplomatic traffic (something it would continue to do for another quarter of a century).

The cable was intelligence gold-dust and could be used to persuade America to join the War.

But how could Britain use it – when to do so would reveal both that they were breaking German codes and that they had obtained the message by spying on the very country it was hoping to become its ally?

Find out at the link.