When I was in, LTJG was automatic since no in flight training had yet been winged. Selection to LT was 85%; LCDR 65%, to CDR 55% and so on. Selection to CAPT was much lower; in my year group, it was 6%. Of course, the year you came up for promotion was also important.
Those are about the same percentages we saw in the Army during my years on active duty.