The functional specification of the machine was produced by Max Newman. The main engineering design was the work of Frank Morrell at the Post Office Research Station at Dollis Hill in North London, with his colleague Tommy Flowers designing the "Combining Unit". Dr C. E. Wynn-Williams from the Telecommunications Research Establishment at Malvern produced the high-speed electronic valve and relay counters. Construction started in January 1943, the prototype machine was delivered to Bletchley Park in June and was first used to help read current encrypted traffic soon afterwards.