The military is a hierarchal organization. Promotions into the next rank are (usually) based on merit and seniority. But the rank structure is a pyramid; promotions tend to select the better personnel for higher rank (where there are fewer slots), which equates to leadership positions.

The core of any military is the non-commissioned officer, who rise from the enlisted ranks. Sergeants (petty officers in the Navy) are who actually run the military; they are the first line leaders, responsibile for supervision, direction, and training. Officers are in command, which really comes down to setting the objectives, setting the plan, and then leading the way. There are details, of course, but that's the broad picture.

The soldier breaks into the NCO ranks at buck sergeant (E5; a corporal [E4] is usually an NCO in training). This typically happens after 4-6 years of service. It can be faster in combat. However, most enlistments are 4-6 years (again, this depends on a number of factors, and a recruiter is a better source of information on this). To stay on in the military, the soldier must re-enlist.

That means most of the re-enlistees are *potentially* material for promotion to sergeant. This is not always the case, but the military dislikes the "career privates" that used to be around. Some people would be happy to remain in the military at a lower rank, but that hasn't been the policy. Still, I really don't know what the current policies are, but with the re-enlistments rates quoted in your post, some folks are not going to be sergeants. I can't say how many, but some. But others will be promoted, and go to fill vacancies from promotions, transfers, casualties, etc. So there will be vacant positions to fill in the lower ranks (E1 to E4).

This is what recruitment does. It brings new enlisted personnel into the military to fill those lower ranks. The military stills needs "the hewers of wood and drawers of water" (if I have quoted that correctly), not to mention the private with a rifle kicking in doors on bad guys.

So a high re-enlistment rate with a mediocre recruitment rate is not necessarily bad. The situation does allow for a higher percentage of experienced soldiers at lower ranks, which actually increases a unit effectiveness and readiness (less greenhorns, more veterans). But re-enlistment can't cover the gap forever.

It's important to point out that we have a highly motivated military. I have *never* seen those sort of re-enlistment rates before, and I've 26 years time in service. The recruitment rates, while not spectacular, are excellent when you consider that the economy is in good shape, and there is a good chance that joining up means a tour in Iraq. Yes, people are chosing not to join the military, but that was the case before 9/11. I don't see a major problem here, in my opinion.