Imperial Navy

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, as well as 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 Guard 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 years of the Heresy. This tendency to make use of the power of an Imperial starship combined with that of an Imperial 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 interservice 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 Imperial Guard but only by the members of their own service.

Ship Types 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 crew 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 weapon 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 maneuverability 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 maneuverable 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.

Imperial Fleets
The Imperium of Man is divided into five territorial "Segmentae Majoris": the Segmentums Solar, Obscurus, Pacificus, Tempestus and Ultima. 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 Battlefleet Solar, all the assets in the Ultima Segmentum are Battlefleet Ultima, and so on. There are five Lord High Admirals, one controlling the fleets 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 office. It is not uncommon for one of these Lord High Admirals to sit on the Senatorum Imperialis as a ruling High Lord of Terra.

In turn, 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 starships of each Segmentum are divided amongst the Sectors into 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 a Lord Admiral.

Each Sector Battlefleet is assigned a number of Cruisers and Battleships, usually between 50 and 75 vessels. The Battlefleets are 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 holy worlds of Terra and Mars that lie at the very heart of the Imperium.

Fighter Squadrons
Many Imperial Navy capital starships of Cruiser size and above are capable of carrying squadrons of Attack Craft like starfighters. 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 battleships and heavy cruisers are known to have launch bay capacities of up to 2000 fighter craft, bombers and dropships.

Aerospace 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 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. 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 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 have 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 defense 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 support, 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 Navy aircraft, they are sometimes directly assigned to specialised Imperial Guard Regiments, such as the Elysian Drop Troopers.

During boarding missions and low profile personal movement, the Navy would deploy 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 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 ship's hull, but easily powerful enough to kill. Naval security are famed for their vigorous training and natural skill, second only to Storm Troopers.

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.

Weapon Batteries
Weapons batteries usually are the primary armament for most 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.

Lances
Lances are Imperial directed energy weapons of extreme power. Usually mounted in large and heavily armoured turrets, 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 hull and cutting smaller vessels in half.

Torpedoes
Torpedoes are long-range missiles carried by many Imperial Navy vessels. From ~60 feet (on Destroyers) to ~200 feet (on Cruisers) to ~300 feet (on Battleships) in length, these weapons are powered by a fusion-based plasma reactor which also doubles as its warhead. Once launched, the plasma drive propels the torpedo towards its foe, whilst starting an energy build-up that will detonate the projectile once it reaches its target. Most torpedoes only have limited detection capabilities and will not track and engage its target unless its passes within a few thousand kilometres of the target vessel. 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.

Nova Cannon
A Nova Cannon is a huge weapon. Normally mounted in the prow of the ship so that the ship's engines can compensate for the recoil, these guns use gravimetric impellers to propel a projectile close to the speed of light. After reaching a preset distance, the projectile implodes with a force potent enough to cripple most vessels and/or damage several at once.

Defensive 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 among 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.

The 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 holy 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 maje use of Navigators is unclear. 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.