There's no rhyme or reason regarding ship designations at all. Does "BB" mean a ship designed to fire small plastic pellets using compressed gas? Did they arrive at "DD" and "FF" because they were so nice they had to name them twice? "CV" doesn't mean "Carrier Vessel" as popularly believed but comes from the fact that the USN basically regards carriers to be cruisers (at least at first) and the V is there just because - no, really, the "V" was pretty much chosen at random to designate an aviation-related vessel.
The only designations that have any real logic behind them are "BM" (Battle Monitor, I'm sure it'll come into vogue again when the SecDef thinks we need armored floating cheeseboxes for homeland defense) "CL" (Cruiser, Light), "CG" (Cruiser, Guided-missile), "DL" (Destroyer Leader, now obsolete) and "DLG". You can make an argument for "CA" (Cruiser, Armored, and then their successors, heavy cruisers) but I heard the "A" was pretty much chosen at random, too.