He could do it to show that the victory that they win is  beause of Him rather than their own efforts.

If I am not mistaken, Joan of Arc was an illiterate peasant girl, so the idea of putting her at the head of an army is quite confounding to the men that lose to her troops. As men in war, would you not feel greatly humiliated at being trounced by a young, illiterate, peasant girl? The English were, are, and always have been rather proud people. Does Henry VIII not attest to this? "He hath filled the poor and humble with good things and the rich he hast sent away empty" Also, the fact that there are hardly any other women out there like to St. Joan of Arc quite simply proves the fact of an exception and not a usual circuмstance. You are going to dissapoint a lot of little girls and ruin their dreams if you tell each of them they can be another St. Joan. If you want greatness, become humble. I've seen humility be profitable in my (short) time, even if you don't realize it 'til years later.

Another thing, if people are talking about "gender equality" and appying "gender" to people, yall should all go and study some English! "Words have a gender, people have a sex". Now, if we are going to speak of what words we can use to describe ourselves, then I'm a trans-literate tri-racial supra- normal libral-heabro-phoeb Vetus Ordo Catholic. Pretty fancy, yea? However, I can't change my gender, because I don't have one and neither do you! I can't change my sex either, since the fundamental chromosomes are impossible to modify.

It's sad... people want to play politics and attempt to side-step morality but they can't even speak their own mother tongue correctly! Maybe the reason folks don't seem to have any real logic is because they never learned the meaning of the words they're using. Maybe it's like the e-card: "I don't always know what a big words mean, but I like using them because it makes me feel so photosynthesis." Of course, at this point it also applies to the small words.

To close, I must agree with jvk. Who are we to question God when we can't even begin to speak correctly? If people are too stupid to even see what is and is not natural (or don't want to see), what makes you think they can be reasoned with? What makes you think they actually care what a God they don't believe in has to say on the matter?  Most of these people wouldn't be able to accept that a fish living out of water is the exception and not the rule if it fits their fancy. And that is the point, St. Joan was an exception and not a norm. Yes, everyone has the potential to be a Saint, but not everyone chooses to be. We have it in our power to adhere to a belief even if we don't FEEL like we believe in it. That is what it means to trust, that is what it sometimes means to put faith in a Supernatural Mystery. We have the power to change our own minds and beliefs if we so choose, it's just a matter of how much we wish to commit to those changes. "I do what is hard today so that it shall be easy tomorrow" - Aristotle (?) Those who really want the truth shall continue to search, even if they don't find the answer right away.

My apologies for being a smartass, but that is certainly the way my words come out most of the time. Most especially so if they are printed as they are thought, without a proper draft and/or revision. In any case, that really is one sorry excuse of a post, isn't it? If only it could be deleted I would have!
I apologize for being a jerk about it, though. Thank you for being more patient with me than I was with you. 
Ok. I'll try to stay on topic.
So, what makes you thik that St. Joan is not an ideal soldier? Are you denying that she is? Personally, I believe her to be a good example of what qualities a soldier should have: Faith, Courage, Loyalty, Obedience.
  I'm simply saying that I don't think women are the ideal sex for soldiers or any such position in the military, and I don't think the impression should be given that they are. 
  Faith, to believe in God and the mission he gave her to do. Courage, to leave the safety and comforts of home for the battlefields at a tender age and lead armies when the men who should have been taking command refused to. Loyalty and Obediance, because she fought for her king and country when all the other "generals" wouldn't budge, took the cities she was ordered to and did everything for the common good of her soul, king and country, and refused anything to the contrary.

Just as the Jєωs lost their special position, which was taken by the Gentiles when they rejected Christ, so to wil men likely lose their place in life if they shirk their proper responsibility. St. Joan of Arc is probably more then just an example of whata soldier should be, she may even be a warning to the men of what displacement awaits them if they don't rise to the occasion.

Whatever the situation, I don't think it's natural for women to be soldiers. This is obvious when you think of some of the most basic biological differences between men and women. These differences don't change, and they were created by God for a reason.

What jvk said above about patron saints in the above post is pretty good. Another thing to consider is what it means to be a patron. Most often, in American English, the word is used to refer to one who gives support, which is usually of a monetary form. In this case, why should St. Joan not be a patron of soldiers? If one would pray for her intercession, maybe she can obtain for them the graces needed to be a good soldier. As a commanderess, soldier and Saint, why would she not be interested in helping her fellow Christian troops?

It was a good point, but I still think another reason in being a patron saint is to provide an ideal for which people can strive for in each particular role.