The number of Hamilcars that the War Office required frequently fluctuated. In May 1942 the War Office asked GAL for 360 Hamilcars to be used in two major airborne operations, but this was found to be unrealistic; not only was the production rate for the glider far too slow to accommodate this large number, the same number of tugs needed to tow the gliders could not be found. In November 1943 the War Office issued another report in which it increased the number of required gliders to 800, an even more unrealistic number; by the time production of the Hamilcar ended, a total of 344 had been built. GAL produced an initial run of 22 Hamilcars, which included the two prototype models and ten pre-production aircraft required for evaluation trials. Subsequent production of parts was assigned to a series of sub-contractors called the 'Hamilcar Production Group', which included the Birmingham Railway Carriage and Wagon Company, the Co-operative Wholesale Society and AC Cars. Production for the glider was targeted to begin in late 1941 with approximately 40–50 to be completed by the end of that year; in reality this was overoptimistic, with the planned 40–50 only being completed by June 1944.