For those who aren't aware of the system, here's a short primer (in addition to the link above), using submarine examples. For officers, if you don't get promoted, you're asked to leave the service within a few years. Once you make LCDR (O-4), you're generally allowed to stay around until you're retirement-eligible, but a Lieutenant who fails to promote to LCDR usually has to leave once you fail to select (FOS) twice. This isn't that big a deal -- at the lower ranks, one generally has to be a major screw-up to fail to promote, so you'll normally be doing everyone a favor by taking your talents elsewhere. (On the enlisted side, they kind of have the same concept, but once you make E-6 you're good to go until 20.) It's the officer job career path that, I think, results in some people who are really good at their jobs being forced into jobs where they're not so good.
For a submarine officer's sea tours, you get three years as a division officer, then shore duty. Then you get about 3 years as a Department Head, then more shore duty. About 60% of DHs get selected to do about 2 years as Executive Officer, and about 2/3 of XOs get three years in command. And then, unless you go to new construction or get to fill in for someone who got fired, that's the last time you command a submarine. The best COs get the same three years as the worst, with no time left to start again. (There are obvious exceptions to the above -- I did 5+ years as Eng on two NewCon boats -- but those are exceptions that prove the rule.)
What this results in is people who are really good division officers, but who might be lousy Department Heads, not being able to serve the Navy doing what they do best. On the other hand, if you leave a guy doing Main Propulsion Assistant tours for three out of every five years for 20 years, you take away that slot from a new guy coming up. If the Navy were ever having manning problems that would be an option, but we aren't nearly at that point yet. By constantly injecting "new blood", you end up with people not necessarily filling the job they're best at, but you do get a chance to evaluate all the talent to see who might have what it takes to be a CO. Of course, once you do that, you still get only 3 years out of those guys in command. Is this the best system? The Brits will get guys who are good Engineers be the Eng on several ships for a decade or more, but he'll never get command. There are pros and cons either way.
What do you think? Is "up or out" the way to go, or should we let guys do the jobs they're good at (which would also allow us to reduce accessions)?
Personally, if they would have let me, I would have been happy being an Eng forever.