I tend to assume that "Sector" fleets are the regular Imperial Navy assets present in the Sector.
"Subsector" fleets are local forces, equipped with a mix of IN hand-me-downs, plus locally produced stuff where that is of adequate quality. These forces exist, essentially, as a result of the Imperium's early history, where it assimilated a large number of pocket empires. The naval forces of these pocket empires weren't always able (or willing) to be assimilated into the Imperial naval structure.
The subsector fleets also allow particular areas to provide for their own defence in cases where the Imperial forces are inadequate or elsewhere. In theory, they should have been able to protect their local areas against the Vargr and/or Aslan, when Imperial forces were withdrawn during the Rebellion, or the Solomani Rim War for that matter. Of course, in the Rebellion, many of them were probably drawn into the civil war themselves, guaranteeing that they would be unable to carry out their notional role.
Planetary navies are vaguely similar. In most cases they are coast guard type operations. Some systems can support monitors, which in some cases are the equivalent of Imperial battle riders. Few of these systems would support tenders to allow them to transport these through jump space, but there might be the odd Really Big Civilian Freighter that might be pressed into service if need be.
A few worlds own colonies. A few may maintain small squadrons to protect their shipping, particularly if they economically dominate the subsector. A few may be the bases for megacorporate military assets that are laundered by attaching them to a recognised government. And more than a few may have Ihatei fleets working for them as mercenaries.
So major warships and jump capable vessels may well be scattered around a little more freely than might be expected from a first glance at the matter. That still doesn't mean that these things are to be regularly expected in every system, particularly in areas well away from the borders.
"Subsector" fleets are local forces, equipped with a mix of IN hand-me-downs, plus locally produced stuff where that is of adequate quality. These forces exist, essentially, as a result of the Imperium's early history, where it assimilated a large number of pocket empires. The naval forces of these pocket empires weren't always able (or willing) to be assimilated into the Imperial naval structure.
The subsector fleets also allow particular areas to provide for their own defence in cases where the Imperial forces are inadequate or elsewhere. In theory, they should have been able to protect their local areas against the Vargr and/or Aslan, when Imperial forces were withdrawn during the Rebellion, or the Solomani Rim War for that matter. Of course, in the Rebellion, many of them were probably drawn into the civil war themselves, guaranteeing that they would be unable to carry out their notional role.
Planetary navies are vaguely similar. In most cases they are coast guard type operations. Some systems can support monitors, which in some cases are the equivalent of Imperial battle riders. Few of these systems would support tenders to allow them to transport these through jump space, but there might be the odd Really Big Civilian Freighter that might be pressed into service if need be.
A few worlds own colonies. A few may maintain small squadrons to protect their shipping, particularly if they economically dominate the subsector. A few may be the bases for megacorporate military assets that are laundered by attaching them to a recognised government. And more than a few may have Ihatei fleets working for them as mercenaries.
So major warships and jump capable vessels may well be scattered around a little more freely than might be expected from a first glance at the matter. That still doesn't mean that these things are to be regularly expected in every system, particularly in areas well away from the borders.