Spackerman points to this embarassing statement by press secretary Dana Perino:
"Some of the terms I just don’t know," Perino told Fox News's Chris Wallace. "I haven't grown up knowing the type of missiles that are out there: Patriots and Scuds and cruise missiles and Tomahawk missiles. And I think that men, just by osmosis, understand all of these things. And they’re things that I really have to work at — to know the difference between a carrier and a Destroyer, and what it means when one of those is being launched to a certain area."
Most men I know, particularly (non-defense) journalists, can't lovingly detail the differences between missiles. But you know who can? My Aunt Cathy, who's been working on security and defense issues since the sixties. Somehow, that second X chromosome did not prevent her from learning enough about defense to get a PhD and serve in places like the NSA, the Defense department, and the Naval War College.
Women are certainly underrepresented in defense, but they aren't absent, and neither they nor the men they work with learned their craft by osmosis. They learned by hard work and study, the same way that other difficult trades are mastered. Presumably that list does not include White House press secretary.