Enigma

Enigma was the German encryption system during the Second World War. The German were so proud of it, the were absolutely sure it was unbreakable. 

24mm f/4.0 1/20s ISO8000, Canon 6d with Canon EF 24-105mm IS USM L-lens

24mm f/4.0 1/20s ISO8000, Canon 6d with Canon EF 24-105mm IS USM L-lens

But they were plain wrong.  

The Polish had already understood, how Enigma worked and gave their knowledge to the British, which were able to build a huge machine (called "the bomb" ) to decrypt the catched sparking claims. Later, they got hand on the Enigma itself (by rushing into sinking submarines) and therefore were able to transcript and decrypt most of the German decryption systems throughout the whole war in Bletchley Park. 

So, an Enigma was something very common (to the Germans) and something top secret at the same time. It was a perfect sample for engineering art and the way the Germans were biased with regards to their and their opponents’ abilities also at the same time. And finally, they never knew that they were hacked. That makes an Enigma a perfect symbol for German warfare at that time.

This particular picture was taken in the Technikmuseum in Berlin. A place worth a visit!

I recommend reading the book Cryptonomicon (Amazon US | Amazon DE) by Neal Stephenson if you want to understand the fundamentals and a lot of historical background with regards to Enigma, Bletchley Park and Alan Turing.