Complex sentence: After June 1940, the work was conducted in England at Bletchley Park under the code name Ultra and by mid- 1943, German Enigma messages regularly were being decoded and the results passed on to senior Allied commanders.
Split into simpler sentences: After June 1940, the work was conducted in England at Bletchley Park and intelligence gained was passed on under the codename'Ultra'. By mid- 1943, German Enigma messages were being regularly decoded and the results passed on to senior Allied commanders.