The Daughters of Mars by Tom Keneally

In 1915, Naomi and Sally Durance, two spirited Australian sisters, join the war effort as nurses, escaping the confines of their father’s farm and carrying a guilty secret with them. Amid the carnage, the sisters’ tenuous bond strengthens as they bravely face extreme danger and hostility—sometimes from their own side. There is great humor and compassion, too, and the inspiring example of the incredible women they serve alongside. In France, each meets an exceptional man, the kind for whom she might relinquish her newfound independence— if only they all survive.

Well researched, well written, more history than novel.

I was disappointed by the ending. He gave 2 alternate endings depending on which sister lived and which sister died of the Spanish Flu.  I would rather he just picked one sister to die.

There was a whole;e big thing of Sally's secret guilt all through the book, that in the end turned out to be nothing major. The story wouldn't have lost anything by that thread being left out.