The first Colossus worked at Dollis Hill in December 1943. Then they took Colossus apart and moved it to Bletchley Park. It got there on 18 January 1944. Harry Fensom and Don Horwood put it back together. Colossus read its first message on the 5th of February. After the first Colossus (Mark 1) there were nine Mark 2 machines. These each had 2,400 valves. They were easier to use. They could be programmed to work at five times the speed of the Mark 1. A Mark 2 Colossus first worked on 1 June 1944.