During the WWI, large numbers of women were recruited into jobs vacated by men who had gone to fight in the war.Some women also worked heavy or precision machinery in engineering, led cart horses on farms, and worked in the Civil Service and factories.This led to women working in areas of work that were formerly  reserved for men,  for example as railway guards and ticket collectors, buses and tram conductors, postal workers, police, firefighters and as bank 'teller' and clerks.Known as 'Canaries' because they had to handle  TNT (the chemical compound trinitrotoluene that is used as an explosive agent in munitions) which caused their skin to turn yellow, these women risked their lives working with poisonous substances without adequate protective clothing or the required safety measures.By 1917 munitions factories which primarily employed women workers produced 80% of the weapons and shells used by the British Army.Though there was initial resistance to hiring women for what was seen as 'men's work', the introduction of conscription  in 1916 made the need for women workers urgent.the employment of married women increased sharply -accounting for nearly 40% of all women workers by 1918 (Braybon 1989: p.49).This did not happen; either the women were sacked to make way for the returning heroes (soldiers) or women remained working alongside men but at lower wage rates.Women's employment rates increased during WWI, from 23.6% of the working age population  in 1914 to between 37.7% and 46.7% in 1918.The unions received guarantees that where women had fully replaced skilled men they would be paid the same as the men  - ie would receive equal pay.New jobs were also created as part of the war effort, for example in ammunitions factories which was the largest single employer of women during 1918.