Future military Short fall

I've been think about this all day.

I believe the US and UK military will face major personel shortages in a few years time which may force them to re-instate national service.

My reasoning is that the guy's out in Afganistan and Iraq will won't out of the armed forces as soon as they get home. Not a problem you might say, there's always people wanting to join up. Well not now, not now people have seen what type of things our armed forces are being sent out to do.
So if more and I mean a lot more people are leaving then are joining they will need conscripts to keep the military at operational levels.

I believe in the UK you can buy your way out before you time is up. The government might even consider offer criminals the chance to join up of goto jail, as far as I know this doesn't happen in the UK, not sure about the US.