Imperial Navy

"If the Adeptus Astartes are the Emperor's wrath, and the Imperial Guard His hammer, then His Holy Navy is His mighty shield."

- Cardinal Kregory Hestor

The Imperial Navy is one of the armed forces of the Imperium of Man. While the Imperial Guard represents the Imperium's ground forces, the Imperial Navy is responsible for the fleets of starships that maintain order between the stars and planets in the Imperium, for all space and air support provided to the infantry of the Imperial Guard, and for transporting those Guardsmen across the galaxy to the Imperium's myriad warzones. The battlefleets of the Imperial Navy are constantly engaging threats both inside and outside the Imperium's borders.

History
During the Great Crusade to reunite all the scattered colony worlds of Mankind beneath the rule of the Imperium of Man, both the Imperial Guard and Imperial Navy were originally a single service: the Imperial Army. Under this form of organisation, each Imperial Cruiser would have a single Imperial Army regiment assigned to it. Imperial Army regimental commanding officers held command over both their regiment and the warship assigned to them, making a single warship a tactically flexible combined arms unit and minimizing the damage to the Imperium in the event of the loss of a starship, its crew and its assigned troops in the Warp. During the Horus Heresy, however, it appeared that some Traitor Army regiments used the power of the starships at their disposal in order to forge interstellar empires for themselves in the fires of anarchy that swept the galaxy during the seven bloody standard years of the Heresy. This tendency to make use of the power of an Imperial starship combined with that of an Imperial Army regiment to establish tyrannies on many worlds led to the eventual split of the Imperial Army into the Imperial Guard and the Imperial Navy to deliberately foster a bureaucratic and inter-service rivalry between the two. The Emperor of Mankind Himself issued a decree before his internment within the Golden Throne that starships could no longer be commanded by the officers of the newborn Imperial Guard but only by the members of their own service.

Origins
The origins of the Imperial Navy lay in the campaigns of the Great Crusade that began in ca. 800.M30. The Great Crusade was the largest and most ambitious military endeavour ever undertaken by Mankind. As mighty and valiant as the hosts of the Emperor were, this epic undertaking would have been entirely impossible without the countless thousands of Warp-capable vessels that transported hundreds of thousands of the superhuman warriors of the Space Marine Legions and many millions of Imperial Army soldiers from one star's light to the next. The Great Crusade saw a staggering array of vessels constructed, reclaimed or pressed into service. Some were used for a matter of months before being declared obsolete or wearing out and degrading to destruction, quite apart from losses incurred in battle, while others gained a permanent place in the canon of war, with successful designs endlessly copied and modified as the decades progressed. The first vessels to enter the service of the Imperium were constructed in the orbital foundries of Terra, and later Mars' Ring of Iron and the orbital shipyards of Saturn, under the scrutiny of the Emperor and the Forge-wrights of the Mechanicum, and indeed it was only that in alliance with Mars that the trans-solar expansion was possible in any meaningful way. This was further aided when at last the Saturnyne Dominion, with its accomplished ship-masters, joined the Imperium after their alien overlords were overthrown, and as the Imperium expanded, many more great shipyards were added: Voss, Grulgarod, Lorin and Cypra Mundi, all grew to near rival Mars itself in voidship production.

Driven by the will of the Emperor, the first Expeditionary Fleets pushed outwards into the galaxy. Preceding each great Expeditionary Fleet of hundreds, sometimes thousands, of vessels often ranged smaller contingents of independent flotillas led by a class of martial leader that would become known as the Rogue Traders Militant. Many of these individuals were former rulers of the numerous realms the Emperor had cast down first during the Unification Wars and later as the Great Crusade spread, formerly independent human worlds. They were offered a stark choice--bend their knee before the Emperor and swear service to the Great Crusade, or die by His hand. Though many set pride before what they regarded as slavery, others chose service and took up the Emperor's Warrant of Trade. There was a price, however. The Rogue Traders Militant were expected to scout ahead of the leading edge of the Great Crusade, accompanied by their own armies as well as whatever assets had been ceded them by the Emperor. Operating so far ahead of the Emperor's crusading armies, the Rogue Traders Militant could expect little or no aid should they encounter foes too powerful for them to overcome. After several Terran decades penetrating the inky black of the void, Rogue Trader Militant fleets often appeared as ramshackle vagabonds, many of their starships taken from defeated enemies, sometimes including xenos vessels of entirely novel or esoteric form. They were forbidden to return to Terra, for in His wisdom the Emperor sought not to just rid Himself of powerful rivals, but to ensure that even in their deaths they might serve Mankind. Many vanished alone and unheralded; slain, consumed or enslaved by nameless xenos abominations far form the light of Terra.

As the Imperium expanded, so too did its fleets. Countless long-lost wonders of technology were recovered, some wrested from the dead hands of unwilling custodians, and others surrendered willingly as fitting tribute to the Master of Mankind. Some vessels were unique, constructed by methods even the most accomplished Adepts of Mars could not hope to replicate: the Terminus Est, the Nicor, the Mirabilis and the Phalanx foremost among them. Other patterns and classes proved possible to reproduce and replicate, and before long the various arms of the Imperium's military acquired their own distinctive panoply of warships. Those of the Legiones Astartes were often blunt of prow and slab-armoured, built to endure the withering storm of fire that accompanies a planetary invasion, their plasma furnace-hearts powering some of the most destructive weapons known to Mankind. But beyond these practical needs, each fleet favoured the nature of its Legion, from the sable black marauders of the Raven Guard to the baroque crimson and gold battlecruisers of the Blood Angels to the brute functionality and unadorned steel of the Iron Warriors' siege-barques. The ships of the Emperor's wider naval armadas were more diverse affairs, built for void supremacy. They ranged from stately battleships, multi-kilometre long engines of doom, their armour concentrated to the fore and their flanks repleted with rank upon rank of broadside batteries, to lithe and deadly destroyers and stripped-bare Warp Runners, to watchful piquet frigates and lumbering star-fortresses. Beyond these were innumerable classes of transports, arks, conveyers and supply ships, the forge vessels of the Mechanicum and their own strange space-going engines of war.

Holy Fleet
On many Imperial planets, the Imperial Navy is often referred to as the "Holy Fleet." The Ecclesiarchy preaches that the Fleet is an extension of the God-Emperor's divine will and is therefore itself a sacred institution. This is due to the intimate relationship between the Navigators who are able to guide the fleet though the Warp using the psychic beacon emanating from the Golden Throne and the Astronomican. Whether or not the title applies to all starfaring vessels in the Imperium that make use of Navigators is unclear, though this is unlikely. The Adeptus Mechanicus would also no doubt consider the vessels themselves holy. However, this is due to their own techno-theological beliefs concerning the divinity of all machines.

Imperial Navy Organisation
The Imperium is divided into five fleet zones known as the Segmentae Majoris. Every starship of the Imperial Navy is assigned to one of these Segmentae, and falls under the command of the respective Lord High-Admiral who commands all the Imperial Navy assets of that Segmentum. The naval assets of an entire Segmentum are named after that division of the Imperium; i.e. all of the Imperial fleet assets in the Segmentum Solar are known as the Battlefleet Solar, all the assets in the Ultima Segmentum are the Battlefleet Ultima, and so on. There are five Lord High Admirals, one controlling the assembled Battlefleet of each Segmentae. Although all 5 High Admirals are ranked equally, command of the Segmentum Solar is considered the oldest and therefore the most prestigious and senior posting. It is not uncommon for one of these Lord High Admirals to sit on the Senatorum Imperialis as a ruling High Lord of Terra. All Imperial shipping, civilian or military, is supervised within the jurisdiction of one of the five Segmentae. Each Segmentum has an orbital headquarters called a Segmentum Fortress which forms the base of fleet operations within the Segmentum. The Segmentum Fortress is controlled directly by a high-ranking official of the Adeptus Administratum known as the Master of the Segmentum, who reports only to the Master of the Administratum.

Sectors
Each Segmentum is divided into Sectors, regions of space that are generally cube-shaped and contain 8 million cubic light years of space. These Sectors contain multiple Sub-sectors, collections of star systems no more than 20 light years in radius. The Imperial Navy starships of each Segmentum are divided amongst the Sectors into further groups called Battlefleets. These Battlefleets are assigned the task of safeguarding the Sector they are assigned to, and each Battlefleet is generally named after the Sector it protects (Battlefleet Gothic is located in the Gothic Sector, Battlefleet Calixis is in the Calixis Sector, Battlefleet Cadia is located in the Cadian Sector, etc.) and commanded by an officer with the rank of Lord Admiral.

Sub-Sectors
Sectors are further divided into Sub-sectors, usually comprising between 2 and 8 star systems within a 10 light year radius (some may encompass more systems), while others are smaller in size and are governed by the practical patrol ranges of Imperial warships. Because Sub-sectors ar actually astrographic divisions of worlds (rather than volumes of space) there are vast numbers of star systems within each sector which do not fall within a Sub-sector. These are formally referred to as Inter-sectors -- and are more commonly known as wilderness zones, forbidden zones, empty space, wild space and frontier space. Inter-sectors may contain gas or dust nebulae, inaccessible areas, alien-controlled star systems, unexplored star systems, uninhabited star systems and uninhabitable worlds.

Imperial Battlefeets
Each Sector Battlefleet is assigned a number of Cruisers and Battleships, usually between 50 and 75 vessels. Each Sector Battlefleet is also assigned multiple squadrons of Escort starships, and is also in command of a large number of transports, messenger craft, orbital defences, space platforms and system patrol vessels. The ships of a Battlefleet must constantly patrol their Sector and fulfill a variety of roles; protect Imperial merchant shipping from pirates, transport Imperial Guard regiments to warzones, escort Adeptus Mechanicus Explorator fleets on their voyages to the Imperial frontier and provide orbital support for invading or defending armies.

Because of the vast volume of space that requires policing, a Sector Battlefleet is normally split into detachments called Battlegroups consisting of one or two Cruisers, accompanied by a squadron of Escorts. If a particular situation is more than one Battlegroup can handle, additional detachments of Battlegroups or squadrons are called in to reinforce.

On occasion, an entire Battlefleet can be formed to operate in a smaller area than an entire Sector. Battlefleet Armageddon is assigned solely to the Armageddon Sub-sector, and, prior to the Third War for Armageddon, was made up of 4 Battleships, 27 Cruisers and 36 squadrons of Escorts. Battlefleet Solar is assigned specifically to the Solar System, and is primarily charged with defending the two sacred worlds of Terra and Mars that lie at the very heart of the Imperium.

Bastion Fleets
Even within a single Segmentum, battlefleets can vary massively from sector to sector having been shaped over the course of millennia, responding to their own particular need and circumstance. For example, Battlefleet Gothic forms a component part of the Segementum Obscurus battlefleets, as do its neighbours, Battlefleets Tamahl and Odessa, as well as the more distant Battlefleets Cadia, Agripinaa, Scarus and Corona, among others. Even though these battlefleets all hail from the same Segmentum and rely on many of the same Forge Worlds and naval bases, there is still great variation within them in terms of composition and number of warships.

Battlefleets Cadia, Agripinaa, Scarus and Corona, in particular, are collectively known as the Bastion Fleets. These fleets are given over to guarding the region of space in the Segmentum Obscurus around the Eye of Terror, or the Sectors Ocular as these bordering regions are sometimes known in the Administratum. By their very nature, the Bastion Fleets are some of the most extensive and best equipped battlefleets of the Imperium, forced to exist in a state of near perpetual warfare against the frequent Chaos raiders from the Eye of Terror. More rarely, these battlefleets are forced to assemble into vast armadas and repel the amassed threat of a Black Crusade, and to this end maintain substantial reserve fleets ready for action with the existing active duty fleets of the Imperial Navy when dire circumstances require their use.

Reserve Fleets of the Segmenum Obscurus
As with all highly militarised zones, it is important for the Imperial Navy to maintain substantial reserves of vessels around the Eye of Terror, ready to deploy as reinforcements should the need arise. Whilst it is possible to keep the vessels themselves ready in this manner, Battlefleet Obscura simply does not possess the manpower to keep reserve crews stationed aboard these vessels as well. Instead, whole shipyards are filled with rows of silent, inactive vessels, often representing classes of ship now outdated or scarce. In times of great need these warships will then be brought into service and crewed with ratings from destroyed or crippled vessels or even with hastily mustered new recruits, meaning the crew is unlikely to have any familiarity with their new vessel. A posting to a reserve fleet is an unnerving duty, forcing a rating to enter deep into an unfamiliar vessel which may have lain dormant for many standard centuries. Much superstition surrounds such fleets and perhaps because of this, unusual behaviour of both crew and vessel in these fleets is rather too commonplace. Reserve fleets are used only reluctantly by the Imperial Navy, and only in the most desperate of circumstances, but an invasion the size of Abaddon the Despoiler's 13th Black Crusade in 999.M41 without doubt qualifies as exactly that -- the most dire of circumstances, the most desperate of times.

In a reserve fleet, all vessels are prone to certain unexpected events, such as mass panic or even mutiny amongst the crew, inexplicable noises, sensor readings and sightings or disconcerting setbacks and failure of machinery. Against Chaos warfleets, where the followers of the Dark Gods are able to exert their influence to further unsettle their already nervous opponents, unforeseen events can be even more devastating to ship morale.

Notable Imperial Navy Battlefleets

 * Battlefleet Agripinaa
 * Battlefleet Armageddon
 * Battlefleet Bakka
 * Battlefleet Cadia
 * Battlefleet Calixis
 * Battlefleet Corona
 * Battlefleet Corribra
 * Battlefleet Gothic
 * Battlefleet Koronus
 * Battlefleet Scarus 
 * Battlefleet Solar

Vessels of the Imperial Navy
The fleets of the Imperial Navy are made up of multiple vessels that can be divided into three broad size categories: Battleships and Grand Cruisers, Cruisers, and Escorts. The actual size of starships in the Warhammer 40,000 universe is debatable, however it is worth noting that the upper size of an Imperial Escort mentioned is 30 kilometers from the Black Library story "Wolf Pack" by Gordon Rennie, though the HDMS Lord Solar Macharius is noted to be just 3 kilometres long. The general consensus is that in the Warhammer 40,000 universe, Imperial Escort vessels are anywhere between 750 metres and 3 kilometres in length, Cruisers are anywhere between 5 and 6 kilometres long and Battleships anywhere between 6 and 8 kilometres.

Battleship
Battleships are truly massive starships, equipped with enormous numbers of weapons and potent Void Shields, and usually serve as the flagship for an Imperial Lord Admiral, though this is not always the case. Although very powerful, Battleships are slow and cumbersome to maneouvre. The Imperial Navy employs three main classes of Battleship: the Emperor (which can carry an immense amount of Attack Craft in addition to its normal weaponry),the Victory (known for its heavy Lance batteries) and the Retribution (which is noted for its powerful broadside firepower and its large number of torpedo tubes). The Battleships of Battlefleet Armageddon are based on the older Apocalypse and Oberon-classes. Other Segmentae's battlefleets may rely on yet other starship classes, but the Emperor and more recent Retribution-class vessels are by far the most common Battleship classes in the Imperial Navy. Imperial Battleships can have crews of anywhere between 25,000 to 3,000,000 men or more depending on the source consulted, including large numbers of Imperial Navy armsmen (marines in modern parlance) to defend against enemy boarding assaults. Battleships can be up to 8 kilometres from prow to stern and displace billions of tons. Because they represent such a vast expenditure of resources to construct and require a fairly advanced technical base to maintain, Battleships are typically constructed only in the largest Imperial shipyards in orbit of the major Adeptus Mechanicus Forge Worlds. These vessels are precious assets of the Imperium and are carefully husbanded, usually employed in only the larger fleet formations and the most critical engagements.

For the Imperial Navy officer class (admirals, captains, commanders, first lieutenants, etc.) onboard, an entire section of a large Battleship's command deck may be divided into huge, luxurious staterooms, with vast bedrooms, offices and wardrobes, bathrooms and toilets mirroring those of an Imperial Planetary Governor's palace, and even harems of concubines and handmaidens. Lower-class bridge officers and chief petty officers would have fairly large, moderately luxurious quarters, and the armsmen, mid-class crewmen and petty officers would all have decent accommodation, generally consisting of a sleeping area, chemical toilet and storage locker. However, the bottom-class enlisted conscripts and slave ratings would have little more than a flea-infested sleeping pallet and a single toilet shared between ten ratings.

Grand Cruiser
Grand Cruisers are smaller than Battleships, yet larger than Cruisers. These vessels are usually much older in design and do not incorporate many of the features that are typical in the more current classes of Imperial Navy vessels, like the armoured prow, and are not quite compatible with current Imperial Navy tactical doctrine. As such, many are retired from active duty, but are still used by the Imperial Navy's reserve fleets. The Avenger-class, with its powerful broadside firepower, is one such example of a Grand Cruiser. There are also some modernised versions of Grand Cruisers in active service, but since these are much larger and more heavily-armed than their predecessors, they are more often classed at present as Battleships. These kinds of vessels are usually purpose-built or modified from Battlecruiser hulls and are not commonly encountered in the Imperial Navy.

Cruiser
Cruisers make up the majority of an Imperial Navy fleet. Though not as powerful as a Battleship, Cruisers are much faster and can still deliver a deadly blow. There are multiple classes of Cruiser, most based on the same general hull design but incorporating different combinations of broadside batteries, Lance turrets and Attack Craft hangars. Examples include the all-round, ubiquitous Lunar-class, the Gothic-class with its powerful Lances and the Dictator-class Attack Craft carrier. Cruisers can carry a crew complement of anywhere between 10,000 and 1,000,000 crewmen (including Imperial Navy armsmen and military police squads), depending on the sources consulted. While Cruisers are still particularly technologically complex, it is not uncommon for them to be constructed on smaller Forge Worlds or any Civilised World that has an orbital shipyard suitable for constructing vessels of their large size. Of particular note was the Lunar-class Cruiser Lord Daros, constructed in orbit above the Feral World of Unloth in 11 Terran years by relying on the forced labour of most of that planet’s population for materials.

A note on Imperial warship classes: while naval warships can be defined along a fairly limited number of classes based on weapon configurations approved by the Adeptus Mechanicus, the physical form these vessels take varies widely throughout the Imperium. For example, a Lunar-class Cruiser constructed above Cypra Mundi in the Segmentum Obscurus may bear little resemblance to a Lunar-class Cruiser constructed above Kar Durniash in the Ultima Segmentum and even less so to a Lunar constructed among the vast shipyards of Mars' Ring of Iron. Nonetheless, they will all have roughly the same operating characteristics and weapons configuration, and thus can be easily serviced by any orbital facility throughout Imperial space.

Note there are also classes of Battlecruisers. Although based on a hull-design that is similar to the regular Cruiser types, these starships are generally somewhat larger and more heavily armed, incorporating more advanced power distribution systems capable of supporting Battleship-grade weaponry in a Cruiser hull. A notable example is the Mars-class Battlecruiser, with its fighter bays, broadside batteries, dorsal Lance turrets and an immense, prow-mounted Nova Cannon capable of attacking targets at extremely long range.

A subset of the Cruiser type is the Light Cruiser. These warships fall in size between Cruisers and Escorts, mixing the firepower and durability of the former with the speed and manoeuvrability of the latter. The Dauntless-class is a very common Light Cruiser class in the Imperial Navy. Extremely self-sufficient, it is fast and has enough firepower to be a threat to Escorts and larger capital ships alike. There are other classes of Light Cruiser in common use in the Imperial Navy, most notably the Endeavour-class, which serves in varied forms and hull types throughout the Imperium. Light Cruisers are a fairly common warship class, for they are relatively simple to construct for a capital ship, and they are uniquely suited for reconnaissance patrols and for ensuring a presence where their speed and manoeuvrability are an advantage, and where having a larger number of smaller hulls allows the Imperial Navy to monitor a wider area of space.

Ironclad
Ironclads, much like their contemporary Imperial Navy counterparts, the Battleships, are vast, 8-kilometre-long vessels which lack the Void Shielding of their Battleship counterparts in favour of metres of adamantium plate armour. These warships, built before the advent of Void Shield technology, have since been phased out of production by the Imperium to be replaced by more modern designs. However, those remaining in service have been recommissioned for a variety of purposes; various pattern Ironclads may be retrofitted with a gargantuan, ship-, station- and even planet-killer cannon running the entire length of the ship's keel, linked directly to the stern fusion reactors; others may simply be braced and reinforced for the purpose of ramming into -- and through -- enemy vessels. These starships are rare in the Imperial Navy, due to their archaic design and the lack of facilities still capable of repairing them at existing Forge Worlds, let alone manufacturing new ones.

Escort Ship
Escort ships are the smallest type of warship in the Imperial Navy's fleets, found in two distinct sub-classes. The larger of the two sub-classes of Escorts are Frigates, which are better armed and more heavily armoured than other Escorts. Destroyers are generally smaller than Frigates, but they are by far the fastest and most manoeuvrable interstellar warships employed by the Imperial Navy. They are usually organised in squadrons of 2 to 6 vessels and will always operate as a group or "wolf pack." The main task of Escorts is to serve as a screen for capital starships against enemy torpedoes and Attack Craft so that they can get into position more quickly and safely. They are also employed behind the gun line to finish off enemy Cruisers that have been damaged so that the larger vessels can concentrate on the most dangerous capital ship threats in an enemy formation. Most Escort classes specialise in a certain role, such as the Cobra-class torpedo boat Destroyers or the Firestorm-class Frigate with its armour-piercing prow-mounted Lance. Escorts are normally not more than 1.5 kilometres in length, with Destroyers generally being only 750 metres to 1.5 kilometres from prow to stern.

Commissioned Officers
Commissioned officers represent the highest ranks of the Imperial Navy personnel and their commissions usually can only be granted by the Battlefleet Administratum.
 * Lord High-Admiral - Also called a Battlefleet Commander, Lord High-Admiral is the highest rank of the Imperial Navy. Only five of these august individuals exist, one for each of the Segmentae Majoris. Each is responsible for the Imperial Navy's fighting forces across thousands of sectors in their allotted portion of the galaxy, or in the case of the Lord High-Admiral Solar, the substantial volumes of space around Terra itself.
 * Lord-Admiral - A Lord-Admiral, or Sector Commander, is responsible for all naval operations in a given sector and has direct command of units of the Segmentum battlefleet allocated to that sector.
 * Solar Admiral - Solar Admirals are often prospective sector commanders waiting for assignment to a sector. As such opportunities are rare it is far more common for Solar Admirals to be dispatched to warzones in command of a reinforcing fleet or kept busy on "special duties" with their own independent flotilla.
 * Admiral - An Admiral is allocated command of a portion of a sector's fleet and responsibility for the security of a handful of star systems and the vast tracts of wilderness space that lies in-between.
 * Vice-Admiral - By long tradition, a Vice-Admiral commands the leading division of a fleet, the part that would equate to the vanguard of a terrestrial force. In later times this has come to mean commanding a force of Light Cruisers and Destroyers charged with scouting for the enemy, charting navigational hazards and long-range patrolling.
 * Rear-Admiral - In ancient times when an entire Battlefleet might be massed together, the thousands of starships present would be divided into three commands, each under the command of their own Admiral. The Rear-Admiral was the youngest and least experienced flag officer in the fleet and so would be given charge of the rearmost division as the one least likely to see combat. Over time this flag rank has evolved into a largely administrative post charged with coordinating repair facilities, refuelling ships, forming convoys and other rear echelon activities. Time spent as a Rear-Admiral is seen as essential for a flag officer who aspires to higher ranks to demonstrate their facility with logistics and high-level planning.
 * Commodore - Also sometimes called a Group Commander, the rank of Commodore was originally only a temporary one given to a senior Captain placed in charge of a squadron of starships. Over time the rank of Commodore has found its way into permanent usage as what were once temporary squadrons stabilised into regular patrol routes and areas of responsibility. On rare and terrible occasions when capital ships join together in squadrons the senior Captain is still promoted to Commodore for the duration of the engagement.
 * Lord-Captain - Sometimes also referred to as Flag-Captain, Lord-Captain is an honourific rank normally applied to Captains who command vessels on detached duty.
 * Captain - Imperial Navy Captains are the masters of all that they survey. Aloof and uncompromising, these figures are unbowed by the awesome responsibility entrusted to them. These exceptional individuals hold full command of an Imperial Navy warship and all the souls that reside within it.
 * Commander - A Commander is a subordinate officer rank that is in charge of individual Escort-class vessels, with a Captain or Commodore holding overall command of an Escort squadron. However, an officer with the rank of Commander might also be found as the commanding officer of a squadron of system vessels, wing commander of the Attack Craft onboard a carrier ship, or placed in charge of an orbital station.
 * Lieutenant - A lieutenant is a junior commissioned officer who is usually placed in direct command of system-defence ships and monitors. It is more common to find Lieutenants acting as second-in-command aboard Escort-class ships, as part of the vast bridge crew found on a capital vessel, or in an Attack Craft squadron acting as a Flight Leader. A Lieutenant is regarded as having true potential and the opportunity for for further advancement up the Imperial Navy's chain of command.
 * Midshipman - A Midshipman is the junior-most "officer" rank in the Imperial Navy. Midshipmen are actually better described as students with an officer's rank. Technically afforded an officer's respect, they are nevertheless still in demanding training to become true officers, and many of their duties are "hands-on" opportunities to learn. Midshipmen are so-called because they traditionally have quarters somewhere in a warship's midsection, far from the command bridge.

Warrant Officers
Warrant Officers (also known in some quarters by the archaic term "Petty Officers") act as the equivalent of non-commissioned officers like Sergeants and Corporals in planet-bound Imperial Guard regiments. They disseminate orders from higher authority, ensure that those orders are carried out by the rank and file of enlisted ratings and maintain discipline with regular floggings. They are called Warrant Officers because their rank is created through the issue of a written warrant from either fleet administration or the captain of their warship. Warrant Officers occupy positions of trust on the ship and a Captain with even the most mutinous of crews can keep the ship running as long as he can rely on his Warrant Officers. It is common practise in the Imperial Navy to promote Warrant Officers from among the ratings already on board a warship, but large numbers of warrants are also issued to civilised worlds as part of their Imperial tithe of experienced personnel for the Emperor's military, often with a promise of reward to entice skilled individuals.
 * Ship's Master - The Ship's Master is generally the senior-most Warrant Officer and most experienced voidsman onboard a given starship. Often the master is tasked with critical responsibilities, such as stellar navigation and the keeping of the starship's log. In addition, he or she might oversee the keeping of the ship's attitude jets, hangar decks, and stores and supplies.
 * Gun Captain - A Gun Captain is a highly respected non-commissioned officer who has the great responsibility of commanding a single gun crew on an Imperial warship. The Gun Captain is the foremost expert on performing all the duties of the subordinate ratings in his or her command and often achieves the post only after decades of working his or her way up through all the different enlisted ratings.
 * Sergeant-At-Arms - A Sergeant-At-Arms is placed in charge of a squad of Armsmen anywhere between six and twenty-strong with responsibility for close action in naval combat (such as hit-and-run attacks and boarding actions). A Sergeant-At-Arm's greatest responsiblity is the keys entrusted to him for the weapons lockers found on every deck of a warship. When battle commences the Master-At-Arms signals the Sergeants to clear the decks and prepare for action, indicating at that time whether to arm the crew. Sergeants-At-Arms are often recruited via warrant or planets from among former Imperial Guardsmen to ensure they do not have prior associations with the current crew of their warship.
 * Bosun (Boatswain) - A starship's Bosuns are disciplinarians and taskmasters in a crew, assigned to oversee the common enlisted ratings and indentured workers, determine their duties and ensure that they are carried out efficiently. This often means that Bosuns are responsible for enforcing discipline on recalcitrant crewmembers, and are likely to handle that task personally. This makes them unpopular figures, and aboard many warships they find themselves naturally allied with a ship's Sergeant-At-Arms, as their duties are similar.

Ratings
Ratings are the basic enlisted voidsmen aboard a warship that take care of the menial tasks; hauling shells and missiles, re-routing cables, clearing debris and conducting basic maintenance. Men and women in this class typically have a myriad of sub-classifications (ratings) that specify their role further, e.g. Gun-Layer Third Class, Fuse-Changer Second Class and so on. Ratings make up the great bulk of the starship's crew and will be the ones doing most of the fighting during boarding actions. Contrary to popular belief, many Imperial Navy Ratings are volunteers, for the pay is good and the conditions are better than those on many Imperial worlds. If there are not enough volunteers to fulfill a Captain's requirements he or she always has the right to send Press Gangs to tithe more crew directly from any planet along the way, which may include penal colonies or hab-blocks. In practise, this is often achieved through collusion with the local Planetary Governor, but an Imperial Navy Captain does not need civilian permission to take crew from any world.
 * Armsman - Armsmen are crewmembers trusted to carry weapons at all times onboard the ship and maintain the contents of the weapons lockers. They keep discipline among the lower ranks and protect the crew as needed. Unlike most Ratings, Armsmen get to move around different decks of the warship in the course of their duties and their loyalties are carefully scrutinised. Armsmen are essentially the Imperial Navy's equivalent of marines in the most ancient sense of that term.
 * Voidsmen - Voidsmen (also referred to by the more archaic "Shipmen" on some Imperial Navy vessels) are a warship's enlisted crewmen who possess some training and skill, and are the Ratings most likely to be entrusted with tasks such as conduit-maintenance, bulwark repairs, cog polishing, or other menial jobs that might require some skill and autonomy. Hive Worlders are favoured as Voidsmen due to their familiarity with advanced technology and the fact that they are inured to the worst of the noise and claustrophobic conditions found on Imperial warships.

Indentured Workers
Indentured or slave workers are those unfortunate individuals who rank even below enlisted personnel on a warship and are press-ganged from a world's slums or taken en masse from penal colonies for their ability to perform unskilled hard labour. They are given duties such as hauling guns into position, turning flywheels, and carrying supplies, heavy equipment, and Macrocannon shells. Most ships must replenish their crews of indentured workers every so often, as a steady stream die to malnutrition, accidents and disciplinary actions.

Specialist Ranks

 * Tech-Priest Majoris (Engsinseer Prime) - The Tech-Priest Majoris is the Adeptus Mechanicus representative on a warship's bridge crew and is responsible for communicating the needs of the Mechanicus to the Captain and his officers.
 * Priniciple Navigator (Warp Guide) - The Principe Navigator is the senior-most Navigator on a warship who has the terrible responsibility of charting a passage through the Warp and bringing the starship through unharmed.
 * Chief Astropath - A Chief Astropath is the senior Astropath aboard a warship and has direct dealings with the Captain. He or she is responsible for ensuring that the warship's Astropathic Choirs are able to maintain adequate long-range communications.
 * Master Gunner - The Master Gunner is a high-ranking Warrant Officer given responsibility for the maintenance and performance of the warship's macrobatteries and Lances. He or she is also responsible for ammunition storage and power linkages.
 * Master of Ordnance - A Master of Ordnance is responsible for managing torpedoes and Attack Craft such as huge starbombers, lumbering assault boats and agile fighters carried within a warship's vast launch bays. The Master of Ordnance coordinates the efforts of the deck crews to ensure everything is fuelled, armed and ready to launch at a moment's notice.
 * Master of Arms - The Master of Arms, also called the Master-At-Arms, is charged with ensuring that all weaponry onboard a warship is serviceable and ready for action, from the greatest macrocannon to the meanest Stub Pistol. The Sergeants-At-Arms report directly to the Master of Arms, and by extension all Armsmen are under his or her control, and so they also perfom a role akin to that of a chief of police aboard ship. The Master of Arms is normally appointed from among the commissioned officers on a ship but more rarely a senior Warrant Officer may hold this position.
 * Ship's Surgeon - Also called the Chief Chirurgeon or unofficially, "Sawbones," the Ship's Surgeon is charged with administrating and maintaining the medicae facilities aboard the vessel. A Ship's Surgeon's duties include combatting disease and malnutrition among the crew as well as suturing flesh and setting bones.
 * Officer of the Watch - The Officer of the Watch draws up duty rosters, assigns watches and attends the warship's chronometers. On most Imperial Navy starships the title of Officer of the Watch is rotated through the ranking commissioned officers. On older vessels it tends to become a permanent position assigned to the officer that has served the longest time aboard a vessel.
 * Fleet Commissar - Like their Imperial Guard counterparts, Commissars are appointed to the fleets of the Imperial Navy. Working closely with the ship's Master of Arms, the Fleet Commissar ensures a warship is kept battle-ready at all times and that the crew remains focused on their duty to the Emperor. A Fleet Commissar has the authority to declare a Captain or even an entire crew unfit for service if he or she is sufficiently concerned about their actions or the state of their ship. At least one Fleet Commissar will normally be aboard any capital ship. In the case of Escort squadrons a Fleet Commissar will divide his time between the different vessels in the squadron in a series of snap inspections and drills.
 * Ship's Confessor - A Ship's Confessor is a vessel's Ecclesiarchy representative who works tirelessly to promote the Imperial Creed among the crew and weed out potential Heretics. In these duties the Confessor is usually assigned by lay-preachers chosen from the most faithful on the lower decks. This is particularly essential on large warships as it allows the Confessor to concentrate his or her efforts on the warship's officers, shriving and chastising them as required, reminding them of their duties to the God-Emperor loudly and often.

Fighter Squadrons
Many Imperial Navy capital ships of Cruiser-class size and above are capable of carrying squadrons of Attack Craft like starfighters and starbombers. These are used in a variety of roles, from small fighters providing defence against torpedo attacks, to heavy bombers packing anti-starship ordnance. The largest Imperial Battleships and Heavy Cruisers are known to have launch bays capable of carrying up to 2000 fighter craft, bombers and dropships.

Void Combat
The Fury Interceptor is the most common starfighter used by the Imperial Navy for space combat. With some variants reaching 60 to 70 metres in length, the more common patterns of the Fury are significantly larger than most fighters designed for atmospheric operations, and it carries a three-man crew, including a pilot, navigator and gunner. On occasion, an Astropath psyker will also be aboard, to provide greater communications capability. The Fury's reinforced hull contains an extensive network of circuitry and life-support systems, and even has a small chemical toilet and sleeping compartment for the crew. Furies are normally equipped with multiple forward-firing banks of Lascannons and anti-starfighter missiles. An average Attack Craft carrier can carry upwards of 1,000-2,000 Furies (although most will carry less as to increase their capacity to carry more Starhawks and atmospheric craft), split into fighter wings comprised of roughly 15 interceptors each.

Starhawk bombers are larger, slower spacecraft, designed to carry a heavy payload of Plasma Bombs and armour piercing missiles for use against enemy capital ships in the void. Crewed by a pilot, co-pilot, Tech-priest (plus Acolytes), various turret gunners and a logistics officer, a standard Starhawk features limited sleeping quarters, chemical toilets and even an automated medical unit inside its hull. Armed with a multitude of short-range turret-mounted defence weapons used to fend off enemy starfighters, a lone Starhawk can wreak havoc among enemy fighter squadrons before swooping in to deliver a crippling missile strike on an enemy capital ship. On rare occasions, Starhawks can be modified to carry and launch a very small number of anti-starship torpedoes. A standard carrier warship can carry between 1,000-2,000 Starhawks.

Atmospheric Aircraft
As part of the post-Horus Heresy reorganisation of the Imperial military, all aviation capability and air support in the Imperial armed forces was assigned to the Imperial Navy. No Imperial Guard regiment (with the exception of the Phantine Air Corps and possibly others) has access to aerospace or atmospheric fighter craft, and the assistance of the Imperial Navy is required when air support is needed for an Imperial Guard campaign.

For atmospheric fighter combat, the two workhorses of the Imperial Navy are the Lightning strike fighters and the Thunderbolt heavy fighter. The Lightning is the faster and more maneuverable of the two, but cannot carry as many weapons as the Thunderbolt, and has considerably lighter armour. Lightnings are often used as reconnaissance aircraft and interceptors, while Thunderbolts are mainly assigned to an air superiority role. Both are equipped with vector-thrust capability.

Marauder bombers are huge aircraft, capable of carrying 6,000 kilograms of ordnance. Each Marauder possesses a massive bomb bay and missile racks along the wings, along with a pair of Lascannons and two pairs of Heavy Bolters for defence against enemy fighters. Marauders were the Imperial Navy's original space-borne bomber craft before their replacement by the equally large, but more advanced and heavily-armed Starhawk bomber. The Marauder is also equipped with vector-thrust engines on some patterns, allowing them vertical take-off and landing capabilities. HPAC and SSDC Marauders are equipped with extra ultra-obliteration bombs designed to target heavily armoured targets such as Chaos Space Marines.

For close air support of ground units, the Imperial Navy has access to Valkyrie transports and the Vulture gunship. These aircraft are not true flight craft, instead using vectored thrust to travel quickly at low altitudes. Unlike most Imperial Navy aircraft, they are sometimes directly assigned to specialised Imperial Guard regiments, such as the Elysian Drop Troopers.

During boarding missions and for low-profile personnel movement, the Imperial Navy will deploy a spacecraft known as a pinnace. Pinnaces are unarmed, deep-hulled spacecraft, capable of making an airtight space dock. Normally a pinnace is accompanied by a detail of Naval Security Armsmen dressed in grey and black body armour with their fleet symbol on their chest and gold braid edging their epaulettes. They have form-moulded ceramite helmets plus rebreathers, and are armed with compact, short-frame Autoguns, not powerful enough to pierce a starship's hull, but easily powerful enough to kill. The troops of Naval Security are famed for their vigorous training and natural skill, second only to that of Imperial Guard Storm Troopers.

Weapon Batteries
Weapons batteries usually are the primary armament for most Imperial warships. Since each battery consists of numerous ranks of individual weapons, whole sections of the starship's hull can be covered by gun ports, launcher systems, turrets and weapon housings. The weapons employed vary immensely: Plasma Projectors, close-range Missile Launchers, Laser Cannons, Rail Guns, Fusion Beamers and Graviton Pulsars have all been found on Imperial warships. These batteries fire in coordinated salvoes, to increase the chances to hit and the amount of damage done to a target.

Macro Weaponry
Macro weaponry serves as the baseline starship weapons for Imperial warships. Ranks of large cannons or other weapons destroy their targets through powerful broadsides and volumes of fire. Types of Macrocannons used by Imperial warships include:
 * Disruption Macrocannon - This macrocannon variant fires a "shell" of highly-charged, ionized deuterium atoms. These particles cause minimal physical damage to their targets. Instead, they are intended to overload and shut down power transfer systems throughout the target vessels. These weapons are particularly useful for vessels that need to capture their prey intact.
 * Hecutor Pattern Plasma Battery - The Hecutor Pattern plasma battery is an ancient variant of plasma macroweaponry that refocuses the power of the plasma "blast," concentrating it into a compressed photonic packet that can be fired over extremely long distances. It is rare to see these weapons on any but the oldest Imperial vessels, meaning many are found on Heretic vessels lost to the Forces of Chaos millennia ago.
 * Stygies Pattern Bombardment Cannons - These devastating weapons are designed to reduce planetary defences to rubble and support military landings. Most often they use linear accelerators to launch massed salvoes of heavy magma bomb warheads, and though relatively short-ranged, can also be used in naval combat. Often the rumour that orbiting vessels carry them is enough to force a quick surrender.

Lances
Lances are Imperial directed energy weapons of extreme power. A Lance battery is, in essence, a gargantuan Lasgun, usually mounted in a large and heavily armoured turret. Thanks to the available energy from the ship's Plasma Reactor, a Lance can fire prolonged bursts instead of the short "shots" of man-portable las-weapons. Often, a bright shaft of coherent light connects the weapon to its target, hence the name "Lance". Lances use triple or even quad-arranged energy projectors to focus their energy into a concentrated beam, capable of burning through even the most heavily armoured hulls and cutting smaller vessels in half. Lance batteries can be used to either apply sustained firepower to one precise location of a target, or, by slightly moving the projector, "rake" across its target. Multiple batteries often combine these two firing modes, in the hope of overwhelming their target's Void Shields and inflicting massive damage. The many types of Lances include:
 * Godsbane Lance - This is practically an archeotech relic-weapon. The lengthened focus apparatus and quad lense-arrays give the weapon extreme range, to the point that beam dispersion becomes a problem. The technological demands of these weapons is intense, and only the older Grand Cruisers of the most powerful Battlefleets possess the structural requirements to mount them. In fact, similar weapons are more often found amongst the forces of the Archenemy, as they tend to possess older vessels dating back to the time of the Great Crusade and the Horus Heresy.
 * Las-burners - Las-burners are scaled down versions of true Lances, utilising focused, high power laser beams to cut through a starship's armoured plating. Though these weapons do far less damage, the turrets are smaller as well, allowing smaller warships to carry them. However, their relatively small size also allows them to be used in boarding actions, cutting open the outer adamantium hull to allow armsmen access to an opponent's vitals.
 * Mezoa Pattern Hybrid Lance Weapon - This recent development from the Forge World of Mezoa remains highly controversial in naval circles. It substantially sacrifices range, but increases damage potential by integrating an emitter into the Lance design. Some ship's captains have complained that the reduced range requires a change in ship-to-ship combat tactics. This hybrid Lance can also be installed in batteries.
 * Voidsunder Lance Battery - Commonly mounted on the Dauntless-class Light Cruisers constructed in the Calixis Sector and neighbouring sectors, the Voidsunder Lance Battery sacrifices flexibility for raw power. Mounted in massive housings hanging off a warship's prow and rear fins, these weapons provide a Light Cruiser with a ship-breaking punch. However, only Grand Cruisers are large enough to potentially mount these weapons on dorsal turrets instead, limiting their usefulness.

Torpedoes
"...the torpedo salvo plunged towards the Bale Childer, and in a moment what had been a tight formation of warships dissolved into a panicked mass, each ship evading as best it could."

- Excerpt from "Treatise on Naval Tactics against the Hated Yu'vath During the Angevin Crusade" Torpedoes are massive self-propelled ship-to-ship missiles. While expensive to maintain, these weapons possess considerable destructive potential, and many captains use an enemy's tendency to avoid torpedoes to dominate a battle, forcing enemies to move in particular directions. The most common forms of torpedo are over 60 metres long (on Destroyers), 200 meters long (on Cruisers) and 300 metres long (on Battleships) and contains both a powerful warhead and a short-lived plasma reactor similar to, but less stable than, those used by starships and Titans. Each torpedo is built to accelerate quickly from its launching tube into the void, hurtling in a straight line towards the enemy. While many torpedoes are fired to deter enemy movement and thus may never strike, each individual weapon can do significant damage to a voidship, and thus are feared by many captains. Guided by a crude and murderous Machine Spirit (computer) and the calculations of a ship's Master of Ordnance, a torpedo uses basic Augury sensors to scan for the heat from plasma drives, a target silhouette, any electronic output, and even an enemy ship's mass to locate enemy vessels. Once the Machine Spirit acquires its target, powerful manoeuvring thrusters adjust the torpedo's course to intercept. Unlike weapons batteries and Lances, torpedoes cannot be deflected by a ship's Void Shields -- most shields intercept incoming fire based on its speed. Torpedoes travel slowly enough (relatively speaking) that shields will not intercept them and they can pass through these powerful gravitic energy barriers unimpeded. Upon impact, the forward momentum drives the torpedo's body deep into the vessel's structure before the warhead and plasma reactor both detonate, inflicting damage far greater than that of a single Lance strike or macrocannon shell.

The torpedo types employed by the Imperial Navy include:
 * Plasma Warheads - These explosives are the standard armament for Imperial torpedoes. These systems are designed to blast through a starship's armoured hull, using their high speed to punch deep into the target vessel. The plasma reactor that powers a torpedo's drive forces it deep into the bowels of the ship and then overloads, contributing to the fury of the warhead's detonation. This reduces complexity, making their manufacture simple. Thus, these torpedoes are the staple of Imperial Navy warships.
 * Melta Warheads - These weapons are even more feared by starship captains than standard torpedoes. Mercifully rare and extremely brutal, Melta Warheads detonate a precisely-organised series of Melta charges upon impact with a target, burning through hull plating and consuming sections of the vessel's interior in a roiling conflagration.
 * Virus Warheads - In cases when a vessel must be captured intact, but the target's crew are considered expendable, Virus Warheads are considered an ideal solution. Pirates more interested in inert cargo, salvage, and the possibility of expanding their fleet lust after these rare and unstable armaments.
 * Vortex Warheads - Only a few remaining Forge Worlds still maintain the technological craftsmanship to manufacture these rare weapons. The Vortex Warhead is not a crude explosive charge, but an arcane device that tears open a rent in the very fabric of reality, consigning vast chunks of its target to the Warp. The swirling energy within this tear in the fabric of reality immediately draws all matter in its blast radius through it, leaving gaping wounds in the target vessel. When attacked by these torpedoes, word of these horrifying weapons spreads like wildfire through target crews.
 * Boarding Torpedoes - More manned spacecraft than torpedo, these torpedoes fulfill a comparable role to that of assault boats. However, boarding torpedoes are less manoeuvrable and less armoured than assault boats. To offset these flaws, they are also much smaller targets. The crews of a boarding torpedo are able to make minor adjustments to the torpedo's flight path.

Nova Cannon
"If one weapon could be said to exemplify the righteous fury of the God-Emperor's wrath, it would be the Nova cannon."

- Captain Laurent Strophes

Nova Cannons are a classification of exceptionally powerful weaponry that can only be mounted upon capital ships. These extremely powerful weapons can easily wreak vast destruction upon enemy vessels at great range, but are inaccurate and require a stable vessel to fire effectively. Mounted below the heavily armoured prows of Imperial Navy Cruisers and Battleships, Nova Cannons have few equals in terms of their range or destructive power. While variations exists, a typical Nova Cannon consists of an array of potent gravimetric impellers designed to accelerate a projectile to a fraction of the speed of light. Due to the lethal nature of their warheads, Nova Cannon shells are not armed for a fraction of a second after firing, allowing them to travel many tens of thousands of kilometres through the void before they become truly deadly. These projectiles vary more than the nature of the cannons themselves, ranging from sophisticated plasma warheads which burn with the ferocity of a small star for a fraction of a second, to implosive devices which exert destructive gravitational forces upon all those caught within several thousand kilometres of the detonation. In any case, a well-used Nova Cannon is a terrifying thing to face, as much a psychological tool as a weapon. The weapons, however, are often ill-favoured by the Imperial Navy, with most captains preferring to utilise the more traditional torpedoes. Those few who favour the weapon understand that it is difficult to use and often rendered useless at close ranges.

Defensive Weapon Systems
Every Imperial Navy vessel is covered with defensive turrets that fire kinetic projectiles or energy pulses that are designed specifically to destroy incoming bombers and torpedoes.

Void Shields
Void Shields are protective barriers of gravitic or electrically-charged energy that allow all starships to survive the hostile environment that is the vacuum of space. Shields form an invisible band of energy around the vessel, a variable layer of force that can absorb radiation, interstellar dust, particle showers and weapons hits. Shields have a maximum tolerance and can be overloaded by sustained weapons fire, forcing the generators to shut down temporarily to vent the excess kinetic or direct energy.

Armour
Every spacefaring vessel is equipped with a certain amount of physical armour, capable of deflecting direct weapon impacts on the starship's hull. The strength and thickness of the armour varies depending on the starship's size and type -- a tiny Escort ship will have a ribbed outer hull maybe a foot thick or less, while an 8-kilometre-long Imperial Battleship will have three separate, heavily reinforced adamantium hull layers, with a total thickness of dozens of metres. Common amongst all the warships of the Imperial Navy, ranging from Frigate to Battleship size, is the armoured prow, which is massively reinforced and can be hundreds of metres thick on the largest ships as it is also used as a ram. It is capable of deflecting all but the most powerful of strikes to a vessel's bow.

Propulsion Systems
Every Imperial starship is equipped with a fusion-based Plasma Drive for normal propulsion through the depths of space. Running up to a third of the starship's length, the aft section is a mass of drive tubes, engine compartments and plasma reactors. Most Imperial Navy warships employ Warp-Drives to breach the barrier that separates realspace from the Immaterium and allow for interstellar travel. Implosion of these drives can lead to the creation of an unstable Warp rift, such as that which destroyed Hive Fleet Behemoth during the Battle of Macragge in the First Tyrannic War.

Space Hulks
Space Hulks are warped and often Chaos-ridden abandoned starships that have been fused together by the ethereal forces of the Warp. The Ordo Malleus was at one time tracking 600 individual Hulks, but many more are thought to exist thoughout the galaxy. The reason they form is currently unknown. However, they constantly pose a hazard to any star system where they re-enter realspace from the Warp due to their frequently hazardous cargo. Orks are known to frequent Space Hulks, as are Tyranid Genestealers. They are constantly being destroyed as they are found, due to the Forces of Chaos usually having an agent on board. However, it is not uncommon for Hulk Exploration Teams to never return from scouting the interior. All Space Hulks are different, so no single type or size can be used as a basis for interior construction or modeling by the Imperial Navy for assault purposes. Since Space Hulks can sometimes contain valuable archeotech or artefacts, they are often worth exploring for agents of the Imperium despite the inherent danger.