Originally Posted by fantasy09
It would be pointless to recruit new people if they were having to let the old ones go.
That is an extraordinarily common misconception. All the military services run on an "up or out" model. At some point, the people who stay in either get promoted or must separate.
You also have to continue to bring in at least a minimal amount of new people, so that as existing members promote or separate, the service has the manpower to conduct missions. Someone has to man the guard post or turn the wrench or bust down the door.
If you did otherwise, e.g. stopped recruiting because you "had enough people", 3-4 years later as people promote or separate or retire, the service will simply fail. Nobody would be around to do the work all the remaining people must supervise.
If you removed the up or out, what happens is your existing workforce ages in a young person's game. I've seen some of the European armies where age or physical fitness is not a major issue, and it's not a pretty sight.