Imperial Navy Command Structure, Tasks And Doctrine
 
The Imperium is a feudal state. Nobles in high offices determine the fate of their subjects, thereby enforcing the will of the ultimate ruler, the Emperor. The feudal system of the Imperium is fairly hierachical: At the top, the Emperor is in command of every single sophont in Imperial service. One level below himself, the Archdukes of the domains, being somewhat closer to the point of action, have been granted the power to handle any local problem that  the emperor cannot take care of because of the sheer distances that orders would have to pass from Capital to the place of action. Iteratively, there are the dukes, one for each subsector, who have the same function for the Archdukes as the Archdukes have for the Emperor.
By this chain of gouvernment, Imperial Law is enforced upon both starship traffic within Imperial borders and heretic member worlds. The Imperial Navy is the premier tool at the nobility's hands to do that.
a) Command structure

The Imperial Navy is a vast organization for a vast empire. Given the fact that it takes at least two weeks for any off-scene commander to receive a report and issue appropriate orders even at the closest interstellar distance, the IN relies heavily on personal responsibilty and deciveness of the individual on-scene commander, be it a ships's commanding officer, a squadron leader, or a Fleet Admiral. This has proven to be the only practicable way to handle critical situations.
So far, so good. But wars tend to happen at more than one place, and long-term operation requires some kind of coordination of both logistics and personnel. How is this done, and who is in charge if something goes wrong?
The largest unit of organziation within the Imperial Navy is the sector fleet, which is directly under the command of a Sector Admiral. This one again is responsible to his Archduke's staff, led by a Grand Admiral (which is the highest rank an Imperial Navy officer can attain, by the way). A sector fleet is more a level of budget and abstraction than anything else: A sector fleet actually operating as a whole is something that has not been seen for centuries. Sector fleets are named for their sector, such as Corridor Fleet, Vland Fleet.
A sector fleet consists of up to sixteen subsector fleets, usually under the command of a Fleet Admiral. The subsector fleet is solely responsible to the higher levels of the naval chain of command, but in peacetimes follows the orders of its local duke. It is arbitrarily numbered, though some of them have adapted a more or less pathetic "war name" over the centuries, especially in heavily-fought areas like the Domain Of Deneb or the Domain Of Sol, but not limited to those.
At the same level, there are the reserve fleets. These are second choice, usually almost-obsolete ships with not-as-well-trained or not-as-talented crews and officers. It is a public misconception that these fleets are merely training and waiting for the time when the respective subsector fleet is far away and the subsector is under attack by an enemy of the Imperium. In fact, they are additional police forces, similar in function to a "Coast Guard" on many low-tech Imperial worlds: Policing, search-And-Rescue (SAR) and minor piracy suppression.Reserve fleets are usually named after their subsector, such as the Lunion Reserve Fleet.
Both subsector fleets and reserve fleets are divided into several squadrons. While both subsector fleets and reserve fleets have a headquarters somewhere in the subsector, most ships do not stay in that particular system all the time. Instead, they patrol the various systems of the subsector, routinely returning to the headquarters. Mostly, this patrolling is done by individual ships, but
the members of a squadron regularily meet each other for maneuvers or larger operations. A squadron is usually under the command of a commodore or -rarely- a captain. There is no Imperium-wide convention for naming squadrons, mainly because this would imply forcing some structure to the responsible Fleet Admiral that he or she possibly does not see fit with the local needs.
Occasionally, several squadrons, or one squadron, or parts from different squadrons, are assigned a special task. These units are split again after the completion of the task, and are therefore labeled "task forces". These are the most various "levels of organisation", and therefore no customs for the rank of a task force commander or the naming of such task forces has been established.
Below the above, there are the system navies. These are solely loyal to their own world or system gouvernments, but are marginal, compared to even a small reserve fleet. For more information on these see Part Two, System navies.
 

b) Tasks of the Imperial Navy

Most people would say that the premier task for the Imperial Navy is defense of the Imperium. This is both true and misleading. True, since it is what the Navy does both by existing and if necessary by fighting and what its ships are designed for. Misleading, since it is by far not what the Imperial Navy usually does.
In fact, the navy has a number of things to do in every Imperial subsector. Most important, though often underestimated, is what Imperial Navy personnel calls "showing the flag". Ships of the IN regularily visit member worlds to remind the population of their loyalty to the Emperor and to keep in contact with the world. In the days before the establishment of the xboat network, this was in fact the most reliable way to communicate with the subsector capital, and for many backwater regions it still is today. It is rumored that this is also the premier way for the IN Intelligence to gather data on political developments on the member worlds.
An intended side effect of "showing the flag" is the regular opportunity for protection of trade and anti-piracy even in the less developed areas of the subsector. Since the ships of the IN regularily interact with member world gouvernments, they are quickly informed of any new pirates in the system, and can usually demonstrate immediately that crime against trade is a
fruitless buiseness in the Imperium, usually supported by local forces.
Of course, one must not underestimate training. The Imperial Navy has a reputation as being the mightiest and most professional space navy in Charted Sapce, and such must be deserved every day again. In order to be able to do that, regular training and maneuvers are required. This is most often done on the squadron level, but once in two years or so, the subsector fleet meets and excercises its skills as a whole for a week or two. Maneuvers are never done at the sector fleet
level.
Finally, there is a number of less glorious tasks of the Imperial Navy. Tasks that are almost never mentioned in any holovideos, and that would not serve the public opinion about it very well. These tasks include anti-opposition missions (such as orbital bombardment of anti-Imperial guerrilla fortifications), hunting mostly unarmed private "radio station vessels" (who unforgivingly comment in their broadcasts on Imperial gouvernmental actions) and, rarely but in a very determined way, force "Imperial Allies", that is, client states, back into this "alliance" whenever necessary. The latter includes "protection of Imperial ships outside Imperial borders", which is also seen by said client states as a slight thread not to switch sides. Most Imperial Allies not even think of breaking the alliance just because the Imperial navy is remarkably strong near their space. (This is not to say that most Imperial Allies are so by force- but a few have not made the aggreement quite voluntarily.)
 

c) Imperial Navy Doctrine

Of course, the primary task of the IN still is defense of the Imperium. Since long communication lines are an unavoidable side effect of such a large empire, the local commanders must know what they are expected to do in the case of a major assault on Imperial member worlds. Therefore, a strategic doctrine has been established. Note that the following is a
 

Large-scale strategic doctrine

The basic thought for the Imperium's strategists is not the fate of individual worlds, but the fate of the empire as a whole. Economic losses at the fringes are acceptable, as long as the authority of the Imperium is not in doubt and the enemies of the Imperium get what they deserve (that is, in the eyes of the Imperium, of course). In the case of a serious large-scale attack
(most likely to occur with the Zhodani or the Solomani), a unified strategy is needed.
It has been proven many times in the past that action is preferable to reaction in a war. Since the Fifth Frontier war, when Archduke Norris actually used what military scholars had evaluated as being the most effective strategy applicable for the larger-scale interstellar wars, the Imperial Navy has adapted this scheme as its general strategic doctrine.
This doctrine consists of two vital elements: The border fleets and the large fleets from the inner territories of the Imperium. The border fleets are those that are stationed in the outer subsectors of the Imperium. It is they who will have first contact with the enemy, but will generally avoid all-out battles against major invading fleets. Therefore, these fleets are built around cruisers or , as largest units at the frontiers, battleships. Anything larger - dreadnoughts and especially battle rider squadrons- are usually part of the inner fleets.
In the case of a war, doctrine as currently applied will most likely trigger the following strategic moves by the Imperial Navy as a whole: First, the local subsector fleet that notices the attack first will send fleet couriers to both the neighbouring subsectors and the sector fleet command. Second, it will not try to defend any worlds in the local subsector, but leave this task to the system navies and perhaps the reserve fleet, but either re-attack the enemy's territory directly or retreat to a predefined gathering point, where it will meet with other navies from both some of the neighbouring subsectors and the inner
parts of the sector. If it attacks the enemy's territiory in a attempt to disrupt trade, supply and communication lines, the inner fleets and possibly neighbouring subsector fleets will still gather at some safe point deeper into the territory of the Imperium and prepare for the start of the real war. Once this vengeance fleet has reached the required strength, it will search and
destroy the enemy within Imperial borders.
So far the theory. In practical application, it is not that simple at all: Important worlds, either industrial centres or economic or administrative hubs of some kind, must be protected at all cost, contradicting to the Imperial doctrine. On the rare occasion that the invaders can count on some support by local Imperial population, such as expected in the Solomani Rim, for example, giving up territory may be a deadly move to the empire's integrity.
Normally, such regions tend to be over-defended, prepared to hold every single system and crush invading fleets on first sight, as long as budget permits. If this is not possible, the Imperial Navy will be extremely careful about the personnel it sends to such a region, electing only the best from its ranks. Such an assignment is viewed by IN personnel both as an opportunity
for a quick climb of the career ladder and a gratification by itsself for the challenge it usually is.
 

Small-scale strategic doctrine

Aside from large-scale wars of the all-out type, the IN has combat tasks of smaller scale for the average Admiral: Commerce raiding (during larger wars- see above) comes into mind, but this category also includes campaigns against non-Imperial worlds that frequently "host" pirate fleets or other illegal activities. This section will deal with such operations against small groups of systems, or more generally, with operations where no more than a single subsector fleet are involved.
This kind of operations is normally done by a fraction of a subsector fleet, sometimes even no more than a squadron. The exact strategy applied is up to the responsible commander; the term "doctrine" may be a too hard word for this. In fact, all the Imperial Navy does issue for such operations is a number of recommendations. The following is to be understood in exactly that manner.
Generally, larger fleet concentrations tend to have fewer losses both in absolute numbers and in percentages against any foe. Therefore, concentrated operation of all available units is recommended. However, there is a number of possible scenarios where diversion of Imperial forces may be suitable:
-First, when an Imperial fleet or task force is searching for a base or another secret location.  Here it will be a faster method to send the fleet's ships to the possible coordinates in small groups, and every small group to a different place at the same time. Note that it is vital to the success of such a search operation that the fleet commander establishes some kind of communications network so that when the small search groups found the secret location, the feleet can easily gather again. The establishment of a central and immobile HQ, preferably at the centre of the region of space to be searched, might be helpful for this.
-Second, the search for a mobile target such as a clearly inferior enemy fleet or a number of pirate vessels. This is not quite similar to the above; a mobile search target is found as much by applied psychology as it is by logistics. Still the respective fleet commander will want to split your forces and establish a reliable communications network, but you will probably not establish an immobile HQ, since your target would make use of the vulnerabilty that comes with it. Additionally, if you have a larger "core fleet", the fleet commander can bring this fleet to the most probable spots where the enemy might show up next. The fleet
commander should be aware not to place the brain of his or her fleet at the fringes of the area in question, though. The fleet commander should always remeber that the enemy will try to do to his fleet as stated below.
-Third, the opposite event: The Imperial fleet is the inferior fleet. Here it may be suitable to split the Imperial forces into few subfleets and use them to disrupt enemy supply lines. The commander should change locations of his or her fleets on an irregular basis, but at a high frequency- at least every two weeks! If the Imperial forces are inferior, they should avoid a
battle whenever possible.
 

Large-scale tactical doctrine - system battles

The largest theatre that can be called "tactical" is a single star system. Imperial forces operating around a single star (or binaries and trinaries, for that matter) can be controlled via normal speed-of-light-communications. A fleet or squadron operating together in a system can be seen as a unified tactical body - controlled by its central nervous system, the command ship.
Remember that the speed of light is roughly three hundred thousand kilometers (1/5000th of an AU) per second; larger distances result in a growing communications lag, which may finally be larger than by using a jump courier ship within a single system. It is therefore recommended not to split your forces within a single system, and if the Imperial commander in charge sees a necessity to do this anyway, he or she is recommended to choose his or her best subordinate commanders to lead the respective groups.
In fact, most of what has been written about small-scale strategic doctrine above is fully transferable into the large scale tactical category presented here. There is one aspect that has to be covered separately, though: It is normally preferable not to let enemy courier ships leave the system after the arrival of an Imperial force. Therefore, it is normally suitable not to send all Imperial ships to the same planet within a system. If it is known on which planet the Xboat/courier base is, then one fraction of the invading fleet will destroy this base as fast as possible while the main fleet attacks the mainworld of the system. If it is not known, though, one should either gather intelligence data on the subject, or attack at full tactical concentration, since the enemy strategic command will be warned anyway. In any case, blocking all messages about the arrival of the Imperial fleet will be a tricky and ressource-eating effort. It may be worth the price, though.
The most important strategic points within a given star system are the gas giants and water-containing planets. If there is an asteroid belt with a significant number of ice asteroids, they may be important as well: Hydrogen is the most valuable ressource for any jump-capable fleet. Therefore, defending forces tend to be placed in low orbits around gas giants, concealed within said asteroid belts, and mainworld defense is normally capable of attacking fuel skimmers in the atmosphere as well as any larger star ships in orbit.
If there is more than one or two gas giants within the system, the attempt to defend all of these refuelling places may be not worth the cost. In such a case, unless there is an ultimate strategic requirement stating otherwise, defense is concentrated on economic or industrial hubs within the system, allowing enemy fleets to enter and leave the system at will, but not unobserved or unopposed when attacking Imperial economy within the system.
 

Small-scale tactical doctrine

This is where it all leads to. After all that strategic planning and long-range tactical operating, the opposing ships finally will meet each other in the battle zone. Possible scenarios are too widespread and different in detail to cover them all in a unified doctrine. As with small-scale strategic and large scale tactical doctrine, the Imperial Navy prefers to offer some commendations rather than ordering any pattern of activity. Again, the local commanders on the scene have to decide what to do- and how.
It is recommended to use no tight formations, that is, not to assemble all of your ships within the same radius of a possible nuclear warhead explosion. Most commanders prefer a distance of about 3000 kilometers between their individual ships - a rather short distance in space, but long enough for two ships not to be affected by the same nuclear warhead. Unfortuately, for larger fleets this may lead to an undesirable diversion where not all ships might be able to attack a particular target.
Therefore, the circle wall formation has become the most preferred formation among Imperial Navy commanders: The ships are seperated from each other as necessary, but still are as close as possible to common targets. As a variant of this, the sphere formation is sometimes used. The disadvantage of this one is that some of the fleet's own ships might block the line of fire to the target, but the sphere is clearly more flexible in reacting to unexpected attacks from any dirction. The above is not to say that Imperial Navy forces in a battle always mass in a single formation. In fact, they are usually grouped by following one of two philosphies:
- The first philosophy is to have groups of ships be able to counter any attack. Thus every fleet will consist of a core of relatively large combat ships, a periphery of smaller and lighter vessels that will shield the core ships, and a group of very small ships or even boats, usually fighters, that serve as recconaissance craft and flexible forces for first-wave attacks or escape prevention.
- The second philosphy is to have specialized groups of ships. These forces are built out of ships of similar weaponry and maneuverability. The idea behind this is to have the groups be easier to handle by the commander and improve overall flexibility of the fleet as a whole; groups of more maneuverable ships will be able to strike quickly and then return to the more heavily armoured groups behind, seeking protection. (This tactic is preferred against bases and outposts, or other targets that are usually protected by enemy fleets, but not capable of protecting themselves properly.) It is also a preferred way to group Imperial forces when setting up a trap in an asteroid belt or between several moons of a gas giant.