Full points to Doug, thats hut 8 at Bletchley Park where the German Naval Enigma codes were broken during WW2.
Block B:

Alan Turing's office in hut 8, note his gas mask on the desk, Turing used to cycle around with the gas mask on because he suffered from hayfever. You can also see his mug chained to the radiator to deter thiefs - yes, Turing was slightly eccentric:

German four wheeled Enigma machine:

Had a great day at Bletchley, it really is worth the visit if your near the area.
Cheers,
TSC.