Funny I'm reading Decline and Fall of the British Empire [Rise and Fall of the British Empire] (http://www.amazon.com/The-Rise-Fall-British-Empire/dp/031216985X) right now and finished the chapter on WWI not 20 minutes ago. Weird.

On phone so will paraphrase: the British Empire at least had more than enough manpower available. The question was whether to train non-Indian native populations in the craft of modern war. Whites were highly valued as soldiers and did not like fighting next to coloreds of any sort. There was also a big concern about the dangers of teaching Africans and some Asians the craft of modern European war, lest a corps of professionally trained nationalist soldiers be used against white settlers post-bellum.

So while yes, the White ranks were running thin - particularly in the French Army, indigenous soldiers from the reaches of Empire were still mostly held back as porters and quartermasters. There was one story about how the Maori from New Zealand, magnificent fighters, were frustrated at being held on garrison duty in Malta.

So logically, one would expect that if the shortage of white troops grew too severe, native soldiers would fill the combat roles well before the consideration of women.

typed on my iPhone, forgive any typos

Amateur historian here so there are probably more complete answers out there but I do have sources to back me up. The short answer is yes, all the major belligerents were forced to use women to help the war effort. Russia took this the furthest by training and deploying all female battalions to the front lines of the Eastern Front. Where in places like Britain women were put in uniforms in support roles as health workers, tuck drivers and cooks the Russians armed small numbers of women. During 1916 there are records of Russian women writing the military and requesting to serve in the army. Essentially the only women who were actually allowed to serve however were those with husbands or fathers in the service who could pull strings for them. There were notable cases of women serving openly or disguising themselves to join the army. However there were not many of these women and conservative estimates put the number at about forty-nine by the end of 1916. In 1917 after the December Revolution Russia realized it was on the ropes against the Austro-Germanic armies and new tactics were needed. One of these tactics was the creation of the 300 women "Woman's Battalion of Death." The battalion's purpose was not to provide any real boost in manpower or fighting ability but to shame the men into fighting. The logic was that if men saw women could fight and die for Russia with resolve and discipline they would also fight bravely for fear of being lesser soldiers to females. By October 1917 there were 106 "Death Units" ready for war. Support from Russian women for the Battalions of Death that more volunteered than could be recruited. This resulted in the creation of regional women's battalions such as the "First Petrograd Women's Battalion." By September when these new Battalions stopped accepting new recruits there were between 5,000 and 6,000 Russian women in uniform. During the fall of 1917 several of these women's battalions participated in offensives and killed and died at similar rates to their male counterparts. Russia pulled out of the war early in 1918 and the revolution spelled the end of the women's battalions. TL;DR Russia put ~5,000 women on the front lines as a way to shame men into fighting and they preformed about as well as the men did. Sources: I only used "My Death for the Motherland Is Happiness": Women, Patriotism, and Soldiering in Russia's Great War, 1914-1917. Melissa K. Stockdale The American Historical Review, Vol. 109, No. 1 (February 2004), pp. 78-116 But there is a lot more on the internet about the Battalions of Death and Women in WWI in general. Hope this helps.

A good title on the issue of female soldiers is 'From Corsets to Camoflage' - The only armies to use female soldiers (in a combat role) in the great war were Serbia and Russia.

Female nurses had only recently been allowed to serve in the forces, and there was a concern that empowering women in such a way would lead to domestic issues (primarily the call for women to have the vote), let alone allowing them in a combat role. I'm not certain that manpower shortages were ever a national problem, bar serbia. The british army did not rely on conscription until 1916, which points towards the british armed forces having enough male recruits to satisfy its needs.

Women's involvement in support and auxilarly functions was questioned by the establishment/members of the armed forces both before and during the war (not to mention afterwards, although attitudes did change, particularly to nursing staff). This lack of respect and support for women in uniform at all contributed to a refusal to consider women for combat roles (which is a rather modern attitude - bar some historic anomalies).

Serbia and Russia prove the be the exception, primarily it seems, because of their dire situation during the war. Even then, female combatants were drastically in the minority. Most women in uniform during the great war were nurses or ancilary staff.