Women workers trucking clay for brick making in Wales (copied from Winter and Baggett, The Great War and the Shaping of the 20th Century).

Note what we may call the crucial change: "Temporarily, though strikingly, the war altered relations not only between classes but between genders. The imperatives of war production meant that women became an essential component of the labour force. Military call-up left gaps in the workplace; these were filled by the under-aged, the elderly, immigrants and, in particular, women" (p. 130, Winter and Baggett).