Wondering what our board historians would choose from the world of cloak and dagger (or, equally likely, reams of paper!).
By “effective” I mean actually had a real-world impact, changing the course of history in some manner.
For example: the Zimmerman Telegram - intercepted by the British, used to nudge the US into war against Germany in WW1.
Or the Soviet atomic spies, stealing the secrets of the A-Bomb for the Russians.
Another example would be the Allied effort to break the German Enigma code.
Many have rather extravagant effectiveness claims, which may or may not be true (for example: the Soviets were already working on an A-Bomb, they (arguably!) would have discovered its secrets eventually - the real “secret” was knowing in advance that it worked; reading the Nazi Enigma code was a great advantage but subject to all sorts of limitations, etc.).
The goal in this thread is to nominate espionage acts; in another thread, assuming we have takers, we can then argue about 'em and vote on the most effective.
My vote is for the larger ULTRA codebreaking effort by the Allies.
It was extremely effective and useful, both at a strategic and operational level. Pretty much every major strategic and operational operation in Europe, and many in the Pacific had almost as good of intelligence on Axis forces as the Axis had.
This allowed the Allies to know where, when and with what the Axis was planning to attack, and as the war progressed, the Allies knew what Axis forces were where, so they could attack accordingly.
In general this was well used, but in a few cases (Market Garden) it wasn’t pieced together, or well understood in time.
The Double-Cross System was MI5’s counter-intel operation against German spies operating in the UK during WWII. After the war, it was discovered that every such agent had either been captured or turned . Drawn into the scope of this operation was the crazy-man and all-round legend Agent Garbo, whose story is really quite something. The Allies were thus able to control the flow of information back to Germany, which proved useful.
All this was used to great effect as part of the overarching Operation Bodyguard, which was the deception plan to convince the Germans that the invasion of North-Western Europe was going to be at the Pas-de-Calais. This was a success, allowing the Allies enough time to build a beachhead in Normandy, and to break out.
I always appreciated the role of the codebreaking prior to the WWII battle of Midway. The US had partially broken the Japanese code, and had information that Japan was planning a major battle. The US wasn’t sure where it would be, though. They thought that it might be Midway, so they had Midway send an uncoded message that their water purification plant was down. Soon thereafter, a Japanese message was decoded saying that their target was short of water. The battle of Midway ended up crippling the Japanese navy.
Cracking the Japanese naval code (and being able to predict not only the assault on Midway and the Aleutians, but when they’d occur) was a terrific achievement, and may well have shortened the Pacific war by at least six months or so.
Looking back at all these successful spy/codebreaking operations, I’m struck by how little most of them “changed the course of history”, as opposed to speeding victory for the better-prepared cloak-and-dagger side. In the case of the Zimmermann Telegram, for instance, the U.S. was already tilting heavily towards entering the war on the side of the Allies (largely due to the renewed U-boat campaign against merchant and passenger vessels), and even after the telegram’s contents became public, Wilson delayed for months afterward before calling for a war declaration.* Solving Enigma was a significant factor in winning the War of the Atlantic, but so were numerous inventions, hardware and tactics that swung the balance toward the Allies.
*I’m sort of nostalgic for the days when Presidents actually followed the Constitution and sought a congressional declaration of war.
This is exactly the point: to evaluate which acts of espionage actually had the greatest real-world impact. Seems in fact very difficult to do, as espionage is usually only one in a host of factors at work.
Another example would be the Soviet spies in Japan that helped Stalin decide that the Japanese were not going for a “northern strategy”, and so he could move his army in the east to counter-attack against the Germans: sometimes extravagant claims are made for that.
I read Marching Orders by Bruce Lee. He shows that breaking the Japanese Purple code gave the Allies information that Japanese in Germany reported home. Reports on Russian troop movement convinced the US that Russia was gong to muscle in on territory in Asia as they had in Europe, so the war with Japan had to be ended quickly.