Needs no introduction

Enigma.
Actually, there were many. Originally constructed in 1923 and sold commercially it was modified by the Germans for the wartime communications.

Capable of a staggering number of settings that were changed every day, it's simply amazing that anyone managed to crack it, let alone so successfully, and, so frequently.

Have a read on the Internet, because in my mind, without Bletchley, I think I'd be typing this in German.

But the real credit has to go to the Poles, who cracked Enigma first. So much so, that they knew the German invasion was coming, and handed the lot over to the British and French in 1938.

And then kept silent so no one would know.

Such bravery.