During the period from 1943-1945 Japan's big coalmines faces a severe labour shortage. Korean 'colonials' and the Chinese and western prisoners of war were brought in to help meet the dire labour shortage in te coalmines created by conscription, and women who had been sorting coal at he pit-top also found themselves pushed into working on the coalface (Sonoda 1970). This signalled a radical change in policy from large mine owners and their labour overseers, who were forced to address a number of overlapping issues: the shortage of male labour; intensive government pressures to maintain production' and an existing culture of women's involvement in the industry over many years, though mainly in gender separated roles - that is, women worked above ground, while men laboured underground. Pay reflected these circumstances, and men were paid considerably better wages for their work underground. However, because of the wartime labour shortage, women were once more allowed back into the coalface in 1943 in the large mines. In the smaller companies, they had never disappeared from the pits.
Allen, M. (2010). Undermining the occupation: women coalminers in 1940s Japan. Portal Journal of Multidisciplinary International Studies, 7 (2), 1-14.