They're not? What are they part of, then?
This may be a linguistic misunderstanding. In American Navy parlance `the fleet' refers only to operational units: ships, subs, aircraft, and deployable Marines.
Anything not in the operational chain of command (admin staffs, hospitals, bases, shipyards, etc) are not technically part of the fleet, only part of the Navy as a whole.
If said theater is what is covered by one fleet, yes. (And that would be a subsector).
A theater, a fleet, and a subsector are seperate entities and may or may not coincide. For example, consider Dingir subsector during the Solomani Rim War. There may have been many fleets in the Dingir subsector at any given time, all assigned to the Solomani Rim theater. The Solomani Rim theater of war would have been much larger than simply Dingir subsector. Contrarily, a given subsector in the interior of the Imperium may not have had a whole fleet within its' borders.
I thought I'd explained that I used the USN primarily as a source of a guesstimate for the number of officers you need to run a military organization roughly analogous to a wet navy navy with about 300,000 employees. Nothing more. I don't, for example, think a star navy squadron is a direct equivalent of a 21st Century aircraft carrier group.
Yes, but an imperial fleet is only a slice of a much larger organization, whereas the US Navy is a whole. There are several organizational functions which exist only at the HQ level and do not need to be duplicated at the operational level.
So if we were to decide that cruisers with crews of 200 are commanders' commands, where would you put the dividing line between ships captained by commanders and ships captained by captains, in terms of crew size?
It's a force structure question. It depends on the number of O6 billets the IN needs to fill, the retirement rate of O5s, and the desired `neck-down'. If, for example, one-third of any given year group of officers tend to retire at the O5 level, and the IN wants only the top-half of remaining O5s to make O6, then there should be one-third the number of O6 commands as O5 commands. If no one retires as an O5 and the IN only wants the absolute best officers to be O6s, then a 10:1 or 8:1 ratio of O5 commands to O6 commands would be more appropriate.
Taking your notional fleet referenced in the first post of this thread, and assuming a similiar force structure on the admin side, a crew size of 500-1000 seems like an appropriate range, with maybe seven to eight hundred being the best number.
That does not seem to be the way the Imperial Navy does things. If there are two or more fleets gathered together, the senior admiral gives the orders. In that respect, the IN is more 18th Century than 21st Century.
The US Navy uses seniority at the tactical level, but it does not trump the chain of command. For example, at the Battle of Midway, Rear Admiral Ray Spruance was the senior officer present afloat (SOPA), despite having never commanded a carrier force before, and therefore had tactical control of both his Task Force 16 and Rear Admiral Jack Fletcher's (despite the fact that Fletcher had recently fought at the Battle of the Coral Sea and had extensive carrier experience) Task Force 17, but they both still worked for the theater commander, Admiral Chester Nimitz, who was COMPACFLT (called CINCPACFLT at the time).
In 1943, as US industrial producation made such a change worthwhile, the US Navy added `number fleets' to the chain of command. For example, CINCPACFLT (a name fleet), had three subordinate number fleets (3rd, 5th, 7th) assigned. Each of the number fleets had up to 300-550 ships and were comprised of numerous subordinate Task Forces and Task Groups.
Hope this helps,
OIT