“THE SUBTERRANEAN LIFE IN THE BRITISH FRONT”A british soldier prepares to go underground

“THE SUBTERRANEAN LIFE IN THE BRITISH FRONT”
A british soldier prepares to go underground  with diging and oxygen equipment. P.S.: Note the little cage in his hand, it was used to hold a bird inside of it and take it underground. If the bird died, it would mean that there was no more oxygen in the tunel. 

Source: “A Guerra Illustrada”/”La guerre Illustrée”, August, 1918.