Maybe this is a bit gross, and I suck at communicating my thoughts, so I was reluctant to ask. But this question has bugged me before, both as a woman and as someone who is a bit into fantasy, and stumbling across information about Dr. James Barry recently reignited it.
I think anyone who has had them can agree periods are annoying, disruptive, gross, and often painful, even with modern conveniences. I’m aware that in some eras at least, women tended to have them less frequently due to more pregnancies and/or lack of nutrition, but I’m pretty sure they still very much happened, and I can presume they were even more annoying to deal with back then. I can barely get a pad designed to stay put to stay put, the idea of managing with nothing but some most likely dirty rags makes me cringe, especially because if I recall correctly women didn’t wear underpants for a lot of at least western history, and washing out blood is a tedious pain in the neck.
So how is it that in less convenient eras, this was seemingly not much a problem for female soldiers or warriors, when they did happen? Especially, say, the occasional female soldier pretending to be male? Or any women who could not afford to be pregnant often for any reason?
While I doubt there are many sources which can give a definitive, super specific answer, if, for example, I decided I wanted to disguise myself as a man and join the first crusade, what options would have been open to me to deal with them discreetly? What about if women being combatants was normal in my culture, how would I or others deal with it without it being disruptive? In a story I want to write, a girl lives in a castle as a knight disguised as a man, so what options would this girl have? Or was there some biological reason it wouldn’t be a problem?
During WWII close to a million women served the USSR performing basically every duty from fighter pilot to machine gunner, snipers, and drivers. This doesn't Ideally answer your question because these woman were volunteers, and they did not have to hide their identities. That said, being a girl in the army comes with a unique set of challenges even beyond biological ones. One of the best resources for understanding what life was like for these women is Svetlana Alexievich's book 'Wars Unwomanly Face'. I draw the information in this comment largely from the interviews Alexievich published in this book. Its worth reading for many reasons, and this book really gives you an idea of the struggles these woman faced during the war, at home, and after the war too. It is anything but one dimensional. Alexiavich interviewed a number of woman who mentioned these particular struggles, and for Soviet fighting women, there were very few accommodations for such a thing. Men dont get periods and as such the standard kit for soldiers didn't include menstrual products. For many women in frontline units it depended on weather your commander (typically but not always a man) understood what you were going through. If your commander was young and unempathetic you might face discrimination, if your commander was older and had daughters of his own he would have some understanding. Add to this the fact that many of these girls were between the ages of 14-20 when they first went to war, and it was a very real possibility that girls would have their first period in the field. The truth is that they had to make do, and it depended alot of circumstance. In the winter, in combat, you didnt have alot of chances to wash clothes/rags/whatever you might be using, but when you did wash your uniform you'd wash these items also. Many men in the army were unable to empathize with what their compatriots were dealing with, but many did. Early on in the war there was alot of reticence from male soldiers and downright discrimination, after a few years of war those who had survived were much less so. For Soviet fighting women how you dealt with a period depended alot on your role and your compatriots, but they certainly made do. There is a reason why 588W (all women) Night Bomber Regiment was the most decorated unit in Soviet Airforce history.