Initially, entry was confined to the few service trades then open to women, namely MT Driver, Equipment Assistant, Cook, Clerk and Mess and Kitchen Staff. A small number of fabric workers were also employed. By August 1939, additional trades were authorised: Teleprinter Operators, Telephone Operators and Plotters. Without the services of the WAAF, the RAF would have required an additional 150,000 airmen who could not have been obtained as easily as the women and who could only be provided at the expense of other Services or production. The success of the women's Service is all the more remarkable in view of the prejudice against employing women that undoubtedly existed at the beginning of the war.