Encryption Tips from WWII

The Enigma cypher machine used by the German military in World War II is still a tough nut to crack today. The total number of ways it can be configured for every letter is around 150 million million million. That’s enough to keep it beyond the reach of all but the most determined of brute force attacks. 

So how were the late Alan Turing (whose 100th birthday is being celebrated in academic circles this June) and his fellow Bletchley Park code-breakers able to crack the Enigma and provide the Allies with such priceless intelligence?