I would start by informing them that ENIGMA was actually broken by Poland, and they invited the British two weeks before the German invasions to show them how it worked and give them a prototype enigma breaking machine. They didn't want the technique and knowledge in how to break enigma to be lost after Germany invaded. The French also got a copy, and it was actually the French intelligence service that had gathered the initial data and it was unknown to them that this enabled the polish to break ENIGMA.
What turning did was to take the initial prototype they received and build a even more powerful and refined version. In particular he improved the technique so it broke the naval version of enigma which was more complicated than the army version that the polish had broken earlier. This was in part possible because the British had captured a working naval enigma from a German submarine.
(A lot of this comes a book called The Code Book by Simon Singh. The last chapter on modern ciphers is a bit dated but the chapters on enigma was quite good.
What turning did was to take the initial prototype they received and build a even more powerful and refined version. In particular he improved the technique so it broke the naval version of enigma which was more complicated than the army version that the polish had broken earlier. This was in part possible because the British had captured a working naval enigma from a German submarine.
(A lot of this comes a book called The Code Book by Simon Singh. The last chapter on modern ciphers is a bit dated but the chapters on enigma was quite good.