Line of battle[]
The most basic unit in the Imperial Navy was a line of battle, or simply a line. The Imperial Starfleet shaped four to twenty starships into lines, depending on the type of line. Commanded by a captain of the line, the line was the most amorphous level of organization in the Starfleet. The Imperial Starfleet Order of Battle outlined seven types of lines: attack, heavy attack, reconnaissance, pursuit, skirmish, troop, and torpedo. Attack and heavy attack lines aggressively engaged enemy starships in combat, reconnaissance lines gathered intelligence of the disposition of enemy forces, pursuit lines chased and trapped retreating enemies, and skirmish lines harassed capital starships and engaged enemy picket lines, whereas troop lines were designed to haul Imperial troops, and torpedo lines were designed for planetary bombardment.
In addition to the five types of lines, the Imperial Navy considered an Imperial-class Star Destroyer a line in itself. While an Imperial-class Star Destroyer may be able to act as an attack line and its compliment of starfighters as a skirmish line, the decision to give commanders the option to field a heavy cruiser as a line unto itself was more political than tactical. After a naval staff study suggested a Star Destroyer was the field equivalent of the smallest of naval squadrons, the Admiralty decided that, as there were more lines than squadrons, designating the Star Destroyer as a line unit would get them more Star Destroyers. The Admiralty's thinking prevailed.
Lines theoretically consisted of a unit of four ships, commanded by the captain of the line. In practice, however, naval lines began to range from one ship, in the case of an Imperial-class Star Destroyer, to as many as twenty.
Attack Line[]
An attack line consisted from three to six ships depending upon the outfit of ships present; heavy cruisers and other large ships were generally fewer in number in attack lines, whereas light cruisers and frigates were in greater number.
The purpose of the attack line was to engage enemy starships of equivalent size, or, when in the presence of a Star Destroyer or other, larger capital ship, to engage the enemy within range of the Star Destroyer, making sure the Star Destroyer is out of effective range of enemy ships, thus allowing the Star Destroyer to concentrate on destroying any enemy starship rather than focus on defense.
Heavy Attack Line[]
A heavy attack line consisted of a unit of four to eight ships, none smaller than a light cruiser. Designed to be an independent element of maneuver, the heavy attack line would come out even against any like number of enemy ships.
Pursuit Line[]
A pursuit line consisted of a unit of four to ten ships, usually light cruisers or lighter ships, such as corvettes. The mission profile of the pursuit line was to maintain contact with a retreating enemy, often employed against non-hyperspace capable starfighters, or to follow escaping craft long enough to calculate their jump coordinates.
Some missions, such as "beambaiting," as it's called by crew, called for the pursuit line to track Rebel units to a base or a planet known to house Rebel sympathizers. They engaged starships to see if any Rebel units came to their aid, and then employed a fighting retreat to a point where a heavier element of the fleet can jump in from hyperspace. The Empire enhanced this tactic by sending pursuit lines on such missions without any backup, so the Rebels would never be sure whether or not the line is part of a trap.
Recon Lines[]
Recon lines consisted of a unit of two to four ships, operating in pairs or individually. Usually light cruisers modified for greater sublight speed, and trading in half of their laser cannons for superior sensor capability, recon lines were prioritized to find the enemy, retreat without engaging, and return to report on the disposition of the enemy units.
Recon lines became more common by the time of the Battle of Yavin as the Empire equipped more of its larger capital ships with improved hyperwave signal interceptors (HSis) capable of detecting flux shift, which allowed the Imperial Navy to project a ship's destination once it jumped to hyperspace with greater accuracy.
Skirmish Line[]
Skirmish lines consisted of a unit from four to twenty small combat starships, corvettes being the most common. Skirmish lines were tasked with harassing larger starships or else engage in coordinated action against enemy starfighters.
TIE Fighters used skirmish lines as mobile cover, and skirmish lines provided cover fire for the TIEs.
Torpedo Line[]
The torpedo line usually consisted of two torpedo spheres, designed for planetary bombardment.
Troop Line[]
Troop lines consisted of two Evakmar-KDY transport vessels and two escort vessels, usually two Strike-class medium cruisers. A single transport was designed to carry a corps of Army troops, but often carried less than a full corps as subordinate elements were assigned to other vessels.
Squadron[]
Executor and several escorting Imperial-class Star Destroyers.
A squadron was the smallest independent operating unit in the Imperial Navy. Composed by several lines, a squadron was commanded by a Commodore and ranged from 14 to 60 ships, depending upon the composition of the lines in the squadron. A squadron was the largest concentration of ships normally assigned to a single system. Only a direct order from a Moff, Grand Moff, Grand Admiral, or the Emperor himself could gather more ships in a single system.
The Galactic Republic designated units of identical configuration as fleets. Those units were the total naval presence in a sector. Thus, the squadron was a useful measure of the growth of the Imperial military after the establishment of Emperor Palpatine's New Order.
Similar to lines, the Imperial Navy's Order of Battle designated four types of squadrons: light, heavy, battle, troop and bombard. Light squadrons patrolled areas known to be safe with two attack lines, a skirmish line and a reconnaissance line. Heavy squadrons engaged planetary systems that possessed known enemy presences, with either two heavy attack lines, an attack line and a reconnaissance line for situations where the enemy's position and composition was unknown, or with three heavy attack lines and a skirmish line for situations where the enemy was known to be defending a fixed asset.
It was common to assign Victory-class Star Destroyers to the latter type of heavy squadron. Battle squadrons contained an Imperial-class Star Destroyer. In addition to the Star Destroyer, there were at least three lines, two attack lines and one pursuit line, for an average of 18 ships. The mere arrival of a battle squadron, and more importantly, an Imperial-class Star Destroyer, was often enough to squelch a planetary revolt or scare off an armed space-threat.
Bombard squadrons subjugated worlds in open rebellion that had developed planetary defenses including multilayered planetary shields and large planetary guns with four torpedo spheres, a skirmish line, and a pursuit line.
Troop squadrons had two troop lines, an attack line, and a skirmish line for an average of twenty-five to thirty vessels. They were often used as transfer points for Army units, reinforcing or reorganizing the Army complement of other squadrons.
Systems force[]
A systems force combined several squadrons under the command of an admiral. These combined forces were responsible for Imperial Starfleet actions across multiple star systems. Rather than outline specific formations of system forces, the Imperial Starfleet Order of Battle lent flexibility to admirals to pool the whole of their naval resources and shape them as necessary missions required.
Force superiority pooled at least three battle squadrons and a light squadron. With a minimum of three Imperial-class Star Destroyers and nearly 90 other starships, force superiority's mission was to achieve space superiority, defined as, "the complete absence of hostile craft within the orbital space of controlled worlds, and no chronic enemy ship activity within the entire system."
Force escort protected crucial commercial shipments, economically essential space installations or facilities, and hunted down harassing pirates. With at least two heavy squadrons and two light squadrons, force escort was the most flexible of the force pools. Admirals used force escort to run a variety of missions, knowing well that their large starship count and organizational flexibility would allow for their completion. Where force superiority was given the maxim "always send enough", force escort bore the maxim "never send too much".
Transport force consisted of two troop squadrons, a heavy and a light squadron, for an average of eighty ships.
System bombard consisted of an average of one hundred ships divided between three bombard squadrons and a light squadron. If the admiral felt that force superiority has failed to remove hostile craft from the system, the system bombard squadron was augmented with ships from a light squadron.
Force technical services (FTS) consisted of technical and mechanical specialists who were organized by single ships. FTS has eight vessels, often Evakmar-KDY transports, and was devoted to getting the techs where they were needed. FTS could not repair hulks which were dead in space, but they were equipped with tractor beams to return such vessels to deepdocks where they could be repaired. If the vessel was a complete wreck, FTS had salvaging equipment.
Force support handled munitions, consumables, spare parts and equipment for FTS, medical ships, and droid services, and a typical force support unit consisted of one hundred ships. If travelling into a combat zone, force support is given an escort, otherwise they were on their own.
Fleet[]
Where all previous units were generally bound to specific system or set of systems, the Imperial Navy designated a fleet as a "sector resource", allowing it to operate on a sector-wide scale. A fleet was the smallest unit transferred between sectors. With such a large number of units, there were thousands of potential types of fleet alignments. Common fleet deployment types included superiority fleets, assault fleets, and bombard fleets. Other examples of alignments that a fleet might have taken included a deepdock fleet, support fleet, or ordinance fleet. A fleet was almost always under the command of a Fleet Admiral.
A typical Imperial hangar.
Superiority fleets maintained space superiority in sectors with "four or fewer world confirmed hostile to the New Order, and no more than 16 additional worlds with confirmed significant hostile elements", a superiority fleet was deployed. With six Imperial-class Star Destroyers and almost 400 other starships, a superiority fleet was presumed to be a sufficient force for relatively calm sectors.
Assault fleets transported huge numbers of Imperial Army and Navy troops to coordinate ground operations, while maintaining space superiority around the targeted systems. With two transport forces and two force escorts, an assault fleet engaged in massive planetary and system-wide ground campaigns. Typically numbering about three-hundred seventy six ships, and were built to sustain the so-called "1/4/16/64 Plan." The fleet was expected to coordinate and sustain four types of eforts: four continuous operations at the battlegroup level (occassionally shifting troops from other theaters to temporarily reinforce one mission to corps level), sixteen continuous missions of regimental level (with potential for shifting troops to temporarily reinforce one area to a battlegroup), and sixty-four missions of irregular duration at the battalion level or lower.
Bombard fleets contained an average of 416 ships, allocated between two system bombards and two force escorts. Bombard fleets were assigned to sectors where the Empire had determined the probability of repressing the Rebellion in the sector to be less than even. System bombards were used when the Empire would rather completely destroy a world rather than see it fall into Rebel hands.
A deepdock fleet had an average of two-hundred eighty support vessels, plus a force escort to protect the deepdock assets. Deepdock contained two deepdock complexes, the engineering corps, plus two force technical services.
A support fleet consisted of at least five hundred vessels, a qaurter of which were corvette class or smaller, while a quarter of them were Loronar FSCVs (Field Secured Container Vessels).
Sector group[]
A sector group was the sum total of Naval strength which the Empire expected to commit to a normal sector. A High Admiral commanded a sector group, a title usually granted to the Moff who governed the sector. In sectors that were involved in constant and severe naval actions, the high admiral was a separate position from the Moff. A sector group could be expected to contain at least 2,400 ships, 24 of which were Star Destroyers (Imperial-class Star Destroyers were the norm, but some groups contained older model Star Destroyers), and another 1,600 combat starships.