The Navy was big on selection boards. They all operated out of BuPers and they all served the same function: To screen the records of candidates for schools or promotion. The criteria depends on the times.
All officer promotions, other than to lieutenant (junior grade), were screened by a selection board. Selection to LTJG was almost automatic. Selection to lieutenant was nearly automatic, but each year, there were a few JGs who were so hapless as to not warrant selection to LT. If you failed to select to LT, they would look at you the following year, but good luck with that, and you were let go.
Selection was done on the basis of the "year group" of the officers, which was the fiscal year of commissioning. If you were commissioned in fiscal year 1982, you were in Year Group 82.
It worked like this: Say you were in YG 82. The Navy determined what would be the normal point of selection to LCDR, which generally would have been eight years after commissioning. (This was adjustable for different designators; some might select a year earlier, some might select later.) Say that you were a LT in YG 82 and you were due for regular screening by the LCDR selection board in `90. You would first be screened in `89 for "deep selection." Deep selection was basically a free bite at the apple; if you were not selected, it didn't hurt you. Deep selection was available to real superstars and if you were "deep-screened," it was a sign that you were on your way to a storied career, provided you didn't fuck up.
Promotions were effective at the beginning of the fiscal year after selection in order of seniority. The OCS grads who were commissioned early in the year went first, then the big bulge of ROTC and Boat Skool grads, followed by the last OCS classes. (OCS back then had about seven classes a year.)
The next year you would be screened for regular selection. This was the make-or-break point. If you didn't screen for LCDR, your career was on hold. The selection board would look at you again next year, to see if your subsequent fitness report showed that you had gotten your shit together, but late selection was a rarity and was more a sign that the earlier selection board had made a mistake. That was the principal reason for late selection, to catch mistakes made by the selection board in the previous year. (I believe that it was not permitted to be a member of two successive selection boards.) If you failed to late-select for LCDR, you were separated from the naval service (though nowadays, you could cross-deck to the Army and go get your ass shot at).
Prior to the 1990s, promotion to LCDR meant that you were guaranteed your 20 years in for retirement. If you then selected for commander (CDR), you had 23-25 years guaranteed and for captain (CAPT), 25-30 years. The funnel got narrower each step along and it really tightened down for selection to commodore, er, excuse me, "rear admiral lower half."
The surface navy had three other major selection boards. The first was for selection for Department Head, which was commonly called "Destroyer School." This board screened people well before the LCDR selection board. If you failed to select for Destroyer School, you didn't select for LCDR. If you were in Destroyer School and you didn't select for LCDR, they pulled you out of the school right then and there and it was so fast that you'd have thought that Stalin had ordered you purged (I knew of someone who had that happen.)
In the 1970s, selection for Destroyer School was damn near automatic. In the early 1980s, they had so many people backed up in the pipeline for the school that nobody would have made it through the school prior to their regular screening for LCDR. As the Navy generally preferred to have one fitrep as a department head in each officer's record prior to LCDR selection, they rescreened the pool and got rid of a lot of people. Those who were bilged out were told that they would never select for LCDR and they might as well go home sooner, rather than later, and many did.
Screening for XO was done after the department head tours. If you didn't screen for XO, you didn't make CDR. Sometime in the 1980s, the rules were changed so that to screen for XO, you had to have taken both the written and oral test for command-at-sea. And, as you might imagine, if you didn't screen for CO of what was known as a "commander command," you didn't make CAPT.
There were selection boards that operated pretty much below the radar. Two of those were selection to the Naval Postgraduate School and selection to attend the Naval War College. You didn't find out that you were up for them or if you weren't selected, only if you were selected. The Navy formed an engineer designator in the 1980s to keep talented ship's engineers who were not screening for XO or CO, this selection board also operated unseen (unless they chose you).
Supposedly they all operated the same: There were a bunch of senior officers who did the screening and one who operated as the recorder/secretary. They'd pop the records up on a screen, which was easy to do as BuPers kept all records on microfiche cards, and make a decision. Close calls might be set aside for further debate, but for most, pass or fail was done in a matter of minutes, if that long, by near unanimous votes of the selection board.
It took fucking up on a level of "done fucked the Admiral's dog and run over his daughter" kind to not get promoted to `JG.
If I remember correctly, there was one guy who deep-selected to both LCDR and CDR. Six weeks or so into his command tour on a Sprucan, the ship ran around off the acoustic range off Fort Lauderdale. That was the end of his career (I've forgotten both his name and the ship).