Why aren't cavalry called foot soldiers?  Horses have feet

And if men in the Army have arms, do men in the Navy have naves?  Or at least Naval Oranges?  How 'bout women in the navy?  After all, horses have calves (the kind on their legs) whether they're in the cavalry or not, but firemen don't always have fires

and do feminists call the mailman a femaleman?  :D