The introduction of electro-mechanical encoding machines with billions of permutations at the end of the First World War brought a new challenge to code-breakers. Perhaps the greatest threat was the German Enigma machine and its far more complex big brother, the Lorenz machine. Not that this seemed to bother the British government, who were aware Polish intelligence had managed to `break' an Enigma during its testing with the German army. It did, however, bother Admiral Sir Hugh Sinclair, head of the Secret Intelligence Service (SIS/MI6) and all cryptanalysts who realised that the Polish Enigma was only `broken' until the Germans changed the machine's rotor settings, which at the time they rarely did. With some prescience, Admiral Sinclair decided to set up a joint physical base for SIS and the Government Code and Cipher School (GC&CS), settling on Bletchley Park as their new home.