The German armed forces were always checking to see if the Enigma had been broken and modified it along the way with extra wheels and intricate wiring. But they always came back to the conclusion that it was unbreakable and kept with it. Late on Admiral Canaris held a very strong inquiry into the security of the codes and even that showed they felt it to be sound.
There are many documented scenarios of Bletchley reading messages before they even reached the desks of the High Command.
A documentary recently on tv had an interview with an old German ranking officer who said on eventually learning that we had been reading their messages for years, was totally and absolutely astonished. He just couldn't believe it - but had to.