The canary girls were the United Kingdom's trinitrotoluene (TNT) shell makers of World War I (1914–1918). The nickname arose because exposure to TNT can turn the skin orange-yellow (and cause other, more serious health problems), similar to the plumage of the bird, the canary.[1]
Since most men were joining the military, women were required to fill factory jobs formerly occupied by men. The United Kingdom used slogans like 'National Service' or 'Women's Land Army' to encourage young women to join the work force.