We’ve started the new week with more “shocking” revelations that the U.S. National Security Agency, a foreign intelligence agency, is actually conducting foreign intelligence operations. And pretty effectively at that. Thanks to Edward Snowden and his motley ring of collaborators, the world is getting an idea of what NSA does as its main job. Which is seeing and listening to foreign communications.

Last week Snowden’s stolen information revealed that NSA spies on Mexico. This week it’s France. Which is “shocking” only to those who know nothing about the real world of intelligence, or those who have a preexisting hatred for the United States and its close allies (there is considerable overlap between those categories, as we’ve learned in recent months). Since France is famed in spy circles worldwide for its aggressive HUMINT and SIGINT operations against even close allies, the latest Snowden revelations have been met with the biggest of all Gallic shrugs behind closed doors, no matter what Paris may say publicly.

Countries spy on each other. Everybody with the mental functioning of an adult knows this. Or at least used to. Thanks to Snowden, the global media has grown accustomed to a drumbeat of vague assertions about what NSA is said to be doing abroad. Seasoned spy-watchers will notice that what’s appearing in the media is long on sensation and rather short on technological details, and derive their own conclusions.

There’s an old wag in SpookWorld about there being no friendly intelligence services, but that’s not entirely true. I get asked regularly by neophytes to explain how this works in the real world, but I’m not about to divulge secrets, so what I’ll say is this. Outside the Anglosphere SIGINT “Five Eyes” alliance, which dates to the Second World War, everybody really does spy on everybody, at least to some degree. Which is why counterintelligence is so important. On Planet Five Eyes, it’s different, and has been for a long time.

But even this most enduring of intelligence partnerships has not been around forever, and until its establishment in the dark days of 1940-41, when Britain was on the ropes and a German invasion seemed possible, even the Anglosphere spied on each other. It needs to be said that the British spied a lot more on the Americans than vice versa, since British capabilities in HUMINT and SIGINT were superior to what Washington, DC, then had in its espionage arsenal.

As during World War I, British intelligence in the early 1940s was spying on the United States and running covert action programs to get America into the war on Britain’s side, sensibly enough from London’s viewpoint. Indeed, British intelligence had a pretty significant role in securing U.S. entry into the Great War in April 1917, though the real story is even more cunning than Washington, DC, knew or even suspected at the time. It’s a great spy yarn with world-historical impacts.

Anyone even passingly familiar with intelligence history has heard of the Zimmermann Telegram, the infamous German own-goal that played a big role in pushing a reluctant President Woodrow Wilson into the war on the Allied side. Knowing that Germany was at serious and rising risk of losing the war, Berlin’s top diplomat, Arthur Zimmermann, wanted to try to get Mexico into the war on the side of the Central Powers; as Berlin at the beginning of 1917 had decided to recommence unrestricted submarine warfare, Germany’s military and political leadership accepted that the U.S. was eventually going to enter the war anyway, so why not make it as painful for the Americans as possible?

The secret, encrypted telegram from Berlin, with its explosive offer of giving Mexico large chunks of the United States – basically what the Mexicans lost in 1848 – in exchange for entering the war on Germany’s side, pretty much guaranteed that America would enter the war, as it went to more than its intended recipients.

The course of the war shifted dramatically in Britain’s favor on January 17, 1917, when British codebreakers intercepted the soon-to-be-infamous telegram. From the beginning of the war, the Royal Navy’s SIGINT operation in London, known as Room 40, had done an excellent job, first breaking German naval codes and then moving into diplomatic decryption; by the midpoint of the war, Room 40 was able to read a high percentage of Berlin’s encrypted communications.

It soon became apparent to Admiral Reginald “Blinker” Hall, director of Naval intelligence, that he had a true bombshell on his hands. But what to do with it? He immediately ordered the decrypted and translated telegram compartmented and shared on a very limited, need-to-know basis only; few even in Room 40 knew of its existence. The few officials in London who were briefed about the telegram realized that the message had to be shared with the Americans, who were wavering on joining the Allied cause.

But there was a problem. A big problem. At the beginning of the war, the Royal Navy literally cut all the undersea telegraph cables that allowed Germany to communicate with the outside world. Berlin complained that this made it impossible for Germany to take part in any peace discussions that might end the war. President Woodrow Wilson – remember, he was a college professor by trade – kindly offered to let Berlin send its diplomatic messages via U.S. State Department’s encrypted systems.

In other words, Room 40 got a hold of the Zimmermann Telegram because the British were reading U.S. diplomatic traffic. This was something that London sensibly had no interest in letting the Americans in on. So Admiral Hall devised a cunning deception plan that included sending an intelligence agent in Mexico City to steal a copy of the Zimmermann message from the telegraph office. It worked perfectly as the operation was clever and tightly compartmented, and while Washington, DC, including President Wilson, reacted to the German offer to Mexico with appropriate outrage, the Americans never suspected the message’s true origins. (For the full story check out this NSA version of the saga.)

Indeed, the British kept on intercepting and decrypting U.S. diplomatic traffic for many years thereafter. It wasn’t until the eve of the Second World War that William Friedman, the father of modern American SIGINT, realized what the British had pulled off with the Zimmermann Telegram. By then, it was about two decades too late to matter.