What a gem!
Of course, we now know that there have been some notable and well-authenticated cases of women serving as soldiers in pre-modern time in cultures as diverse as
sub-Saharan Africa and
Japan.
Also, the concern about realism is a bit ironic among two authors who fictional works were deeply rooted in the pure fantasy genre. Further, both men lived through World War II, which was a decisive moment in pushing women into roles that had traditionally been reserved for men out of necessity (see, e.g.
Rosie the Riveter). Even Queen Elizabeth II, e.g., did
engine mechanic work in the military as part of her training for the throne.
Of course, women as soldiers are far more common in fiction than in reality. But that has more to do with the reality of the prospective audience for particular works of fiction. Women and girls are much more receptive to works with strong female heroines. And, strong female heroines engaging in combat doesn't repeal men and boys from the audience as they like action and combat, and they enjoy watching/reading about women so long as the activities those women engage are activities that they relate to/engage with.
In the same vein, fiction has long favored heroes and heroines who are in their late teens who are either orphans or have parents who are distant and disengaged, as it is plausible for them to have adventures, this demographic reads a lot and likes to read about themselves, and characters from this narrow demographic don't alienate younger or older readers, or readers with engaged parents in close families.
So, leading characters who are female soldiers (in their late teens or early twenties, without closely involved parents) expand the audience which improves sales which improves author wealth. So they are pretty much the modal main character profile in the action genre.
But, this insight into the commercial side of speculative fiction wasn't widely known in their day and, in any event, wasn't a major driver for Tolkien or Lewis to write. Tolkien's fiction started off with
an audience of his children, and as a creative diversion from
his work in linguistics (Tolkien also had no talent whatsoever for developing romantic interests). Lewis's fiction was branching off from what he would have seen as his main day job as a
Christian apologetic writer (and while Lewis scoffed a bit a female soldiers, he also did write with
more strong female leads who weren't just damsels in distress or princesses than Tolkien did).
Also, it is worth noting that these views are not independent of each other. Tolkien and Lewis were not just contemporaries. They both lived in Oxford, England, knew each other, and were
regular drinking buddies at the pub who would talk about things like this together. I've been to that pub myself.
