The new girl was peering about the tent when Charlotte and Kathleen stumbled in at the end of their shift that July day in 1917. The work itself was exhausting—twelve hours of standing, bending, folding, feeding, bandaging, debriding, cleaning, and sterilizing; only to repeat it all again. Add to that the effort of presenting cheerful countenances to the hundreds of wounded men they passed each day, and it may be understood that their labours were truly Herculean.

Giving a smile to men w...