This is one thing that has me scratching my head, why the military doesn't do more "continuing" contracts, where pistols which are getting worn out get sold on the "used" market, and new ones are bought, on a yearly basis.
As far as the 9mm/.45 debate, really, how often do military people (outside of certain special ops units who do their own procurement) actually use their handguns to fire at an enemy?
When I was on active duty in the early to mid 1980's, I doubt there was any at all, unless it was the MP's on post.
In today's environment, especially in the ultra tight low intensity urban environments -- I still dunno! I haven't BT or DT But if I had to clear a house or a tightly closed arena or maybe in a tunnel situation with tight blind corners... And having to keep collateral damage to a minimum, I'd want a weapon very easily maneuverable and selective with M4's backing me up, of course. Especially in very tight confines.