Colossus design started in March 1943. By December 1943 all the various circuits were working and the 1,500 valve Mark 1 Colossus was dismantled, shipped up to Bletchley Park, and assembled in F Block over Christmas 1943. The Mark 1 was operational in January 1944 and successful on its first test against a real enciphered message tape. Colossus reduced the time to break Lorenz messages from weeks to hours. It was just in time for the deciphering of messages which gave vital information to Eisenhower and Montgomery prior to D-Day. These deciphered Lorenz messages showed that Hitler had believed the deception campaigns, the phantom army in the South of England, the phantom convoys moving east along the channel; that Hitler was convinced that the attacks were coming across the Pas de Calais and that he was keeping Panzer divisions in Belgium. After D-Day the French resistance and the British and American Air Forces bombed and strafed all the telephone and teleprinter land lines in Northern France, forced the Germans to use radio communications and suddenly the volume of intercepted messages went up enormously. The Mark 1 had been rapidly succeeded by the Mark 2 Colossus in June 1944 and eight more were quickly built to handle the increase in messages. The Mark 1 was upgraded to a Mark 2 and there were thus ten Mark 2 Colossi in Bletchley Park by the end of the war. By the end of hostilities, 63 million characters of high grade German messages had been decrypted — an absolutely staggering output from just 550 people at Bletchley Park, plus of course the considerable number of interceptors at Knockholt, with backups at Shaftesbury and Cupar in Scotland. After VJ Day, suddenly it was all over. Eight of the ten Colossi were dismantled in Bletchley Park. Two went to Eastcote in North London and then to GCHQ at Cheltenham. These last two were dismantled in about 1960 and in 1960 all the drawings of Colossus were burnt. Its very existence was kept secret.