They commissioned the first female pilots two years before the Air Farce, and had them flying carrier based fighters in the '90s. Not that that was without controversy; there was a significant scandal when a female fighter pilot was killed in a landing crash that one investigation ruled a mechanical failure and another ruled pilot error. When further revelations were made that she failed her first carrier flight test before becoming the first "combat qualified" female pilot just a few months prior to her death the immediate and natural accusation was that the Navy rushed her flight training due to political pressures.

The argument I've always heard against women on subs is that sub crews basically live on top of each other; it's not so much the concern mixed gender crews may get intimate with each other as concerns that since the whole crew is perforce fairly "intimate" they'd be very likely to end up having regular sex, which isn't really great for combat effectiveness and chain of command (which is also why fraternization is a no-no generally. ) The military doesn't have private showers, space is at a premium on every Navy ship, and nowhere is this more true than on a sub. Maybe if we had more female sailors than male we'd be talking about excluding MEN from subs, but coed subs still sound like a bad idea, not because women are unsuited or men have no restraint but because mixing genders for prolonged periods in very confining quarters is bad for group discipline, and poor discipline in a combat unit is a recipe for massacre.