An interesting one I heard about recently involved German guided missiles. One attack sank the Italian battleship Roma as it traveled to surrender to allied forces.

The missiles were "Fritz X", and they had a bizarre control method where they were essentially designed to track the path of the plane that fired them.

So you fired the missiles then kept flying straight at the target until they impacted.

Weird.

Another one I read about was that our victory at Midway which was the turning point of the naval war in the Pacific came about because we'd broken Japanese codes and thus knew they were focusing there.

This is similar to how the Russians confirmed via a Soviet spy in the British codebreaking team that the Germans were focusing on Kursk.

Not many people know about Kursk, which is weird, because it was one of the largest, if not THE largest, battles in WWII, and it was the turning point of the eastern front and the German advance altogether.

Up until Kursk, the Nazis had been winning most fights and pushing east and west consistently.

But the Russians knew ahead of time that they were going to hit Kursk next, so the Russians built like ten separate defensive lines and manned them with millions of troops and hundreds of thousands of artillery pieces and tanks.

Hitler was advised that maybe focusing on one place for six months before pulling the trigger isn't a great idea, but he was busy being on meth or something, so in the Wehrmacht went.

They made a good showing for themselves too. They MASSIVELY outperformed Russian defenders.

German tanks and infantry each took like a 5:1 kill ratio.

They crushed the first defensive line like it wasn't even there.

And the second.

And the third.

But by like the sixth they were running out of forces and supplies and time.

They finally stalled at like the sixth or the seventh line, and the Russians still had two more behind those.

The Russians staged a quick counteroffensive, a reverse pincer to envelop and cut off the now isolated German lines.

Bam.

Suddenly the Germans stopped moving east.

From that point on, the eastern front began moving west and kept moving west.

It didn't stop until Berlin.

And the only reason it worked was because the Russians knew the German plans months in advance courtesy of a few spies, and kept that knowledge a carefully guarded secret.