Imperial Navy

The Imperial Navy is one of the armed forces of the Imperium of Man.

While the Imperial Guard is responsible for 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.

The Birth of the Imperial Navy
During the Great Crusade, both the Guard and Navy were originally a single organisation: the Imperial Army. Normally each Imperial Cruiser would have a single Guard Regiment assigned to it. Commanding Officers held command over both their regiment and the warship assigned to them, making a single warship tactically flexible and minimizing the losses in the event of the loss of a spaceship in the Warp.

During the Horus Heresy, however, it appeared that some regiments used the power at their disposal in order to forge empires for themselves in the fire of anarchy. This led to the eventual split between Guard and Navy, as the Emperor of Mankind himself issued a decree ordering that spaceships may no longer be led by members of the former.

Ships of the Imperial Navy
Fleets of the Imperial Navy are made up of multiple vessels that can be divided into three broad categories: battleships and grand cruisers, cruisers, and escorts. The actual size of starships in the Warhammer 40,000 universe is debated, 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 from Rennie's noval Execution Hour is noted to be just 3 kilometres long. The general consensus is that escort vessels are anywhere between 750 meters and 3 kilometre in length, cruisers are anywhere between 5 and 6 kilometres and battleships anywhere between 6 and 8 kilometres.

Battleship
Battleships are huge starships, with enormous amounts of weapons and shields, and usually serve as the flagship for the Admiral of the Fleet, though this is not always necessarily the case. Although very powerful, battleships are slow to maneuvre. Battlefleet Gothic employs three main classes: the Emperor (which can carry an immense amount of attack craft in addition to its normal weaponry),the Victory (apraised for its heavy lance batteries) and the Retribution (which is noted for its powerful broadside firepower and its large amount of torpedo tubes). Battleships of Battlefleet Armageddon are based on the older Apocalypse and Oberon classes. Other Segmentae battlefleets may rely on yet other classes, but the Emperor and more recent Retribution are by far the most common in the Imperial Navy. Imperial battleships can have crews of anywhere between 25,000 to 3,000,000 or more depending on sources, 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 and require a fairly advanced technical base, these are typically constructed only in the largest shipyards above the major Adeptus Mechanicus forge worlds. These vessels are precious assets and are carefully husbanded, usually employed in only larger fleet formations.

For the top 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 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 conscripts and slave ratings would have little more than a flea-infested sleeping pallet and a single toilet 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 current Imperial Navy vessels, like the armoured prow, and are not quite compatible with current navy tactical doctrine. As such, many are retired from active duty, but are still used by reserve fleets. The Avenger, with its powerful broadside firepower, is one such example. There are also some modernized versions of grand cruisers in service, but since these are much larger and more heavily-armed than their predecessors, they are more often classed 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 a 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 starfighter hangars. Examples include the all-round, ubiquitous Lunar-class, the Gothic with its powerful lances and the Dictator starfighter and attack craft carrier. Cruisers can carry a crew complement of anywhere between 10,000-1,000,000 and (including Imperial Navy armsmen and military police squads), depending on sources. While cruisers are still particularly complex, it is not uncommon for them to be constructed on smaller forge worlds or any civilized world that has a shipyard suitable for constructing vessels of their size. Of particular note was the Lunar cruiser Lord Daros, constructed in orbit above the feral world of Unloth in eleven years by relying on the forced labor of most of that planet’s population for materials.

A note on Imperial ship classes – while naval warships can be defined along a fairly limited number of classes based on weapon configurations approved by the Adeptus Mechanicus, the form these vessels takes varies widely throughout the Imperium. For example, a Lunar cruiser constructed above Cypra Mundi in Segmentum Obscuras may bear little resemblance to a Lunar cruiser constructed above Kar Durniash in Ultima Segmentum and even less so to a Lunar constructed among the vast shipyards of Mars. 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 cruisers, these ships 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 category are the light cruisers. These ships 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 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 both escorts and capital ships. There are other classes 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 ship class, for they are relatively simple to construct for being a capital ship, and they are uniquely suited for reconnaissance patrols and for making a presence where their speed and maneuverability are an advantage, and where having a larger number of smaller hulls allows the Navy to monitor a wider area of space.

Ironclad
Ironclads, much like their contemporary counterparts, are vast 8-kilometres vessels which lack the void shielding of their counterparts in favour of meters of adamantium plate armour. These ships, built before the advent of void-screen technology, have since been phased out of production, for the main part, to be replaced by more modern designs. However, those remaining in service have been recomissioned for a variety of purposes; various pattern ironclads may be retrofitted with 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 ships are rare in the Imperial Navy, due to their archaic design and the lack of facilities still capable of repairing, let alone producing them.

Escort ship
Escort ships are the smallest type of ship in the Imperial Navy fleets, found in two distinct sub-classes. The larger of the two are frigates, which are better armed and more heavily armoured. Destroyers are generally smaller, 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. The main task of the escort ships is to serve as a screen for capital ships against enemy torpedoes and attack crafts 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 important 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. Escort ships 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 is divided into five "Segmenta": Solar, Obscuras, Pacificus, Tempestus and Ultima. Every ship of the Imperial Navy is assigned to one of these Segmenta, and falls under the command of the respective Lord High Admiral.

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 twenty light years in radius. The ships of each Segmentum are divided amongst the sectors. These Battlefleets are assigned the task of safeguarding the sector they are assigned to, each Battlefleet is generally named after the sector it is assigned to (Battlefleet Gothic is located in the Gothic sector, Battlefleet Cadia is located in the Cadian sector, etc).

Each Battlefleet is assigned a number of cruisers and battleships, usually between fifty and seventy-five 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 fulfil a variety of roles; protect merchant shipping from pirates, transport Imperial Guard regiments to warzones, escort Adeptus Mechanicus Explorator fleets and provide orbital support for invading or defending armies.

Because of the vast space that requires policing, the Battlefleet is normally split into detachments consisting of one or two cruisers, accompanied by a squadron of escorts. If a particular situation is more than a detachment can handle, additional detachments are called in to reinforce.

On occasion, a Battlefleet can be formed to operate in a smaller area. Battlefleet Armageddon is assigned solely to the Armageddon sub-sector, and, prior to the Third War for Armageddon, was made up of four battleships, twenty-seven cruisers and thirty six 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.

Fighter Squadrons
Many Imperial Navy capital starships are capable of carrying starfighter squadrons. These are used in a variety of roles, from small fighters providing defence against torpedo attacks, to heavy bombers packing anti-ship ordnance. The largest battleships and heavy cruisers are known to have launch bay capacities of up to 2000 fighter craft, bombers and dropships.

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 Fury is significantly larger than most atmospheric fighters, and carries 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 4-6 thousand Furies (although most will carry less as to increase their capacity to carry more Starhawks and Atmospheric craft), split into fighter wings of roughly 15 interceptors each.

Starhawk bombers are larger, slower craft, 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 can carry between 1-2 thousand Starhawks, split into bomber wings of about 10 starbombers each. Battleship carriers, such as the Emperor class, would be able to carry several times this number. There is a fan-created version,the Thunderstrike, with a 24-shot rotary missile launcher. It also has a modified cockpit and upgraded sensors. The Thunderstrike (or 'Thud' to crews) is about 20 meters long.

Atmospheric Aircraft
As part of the post-Heresy reorganisation, all aviation capability 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 fightercraft, and the assistance of the Imperial Navy is required when air support is needed for a 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 manoueverable of the two, but cannot carry as many weapons as the Thunderbolt, and are considerably lighter armoured. 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 10,000 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.

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.

Offensive Weaponry
Weapons Batteries usually are the primary armament for most warships. Since each battery consists of numerous ranks of individual weapons, whole sections of the ship'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 been found on Imperial ships. These batteries fire in co-ordinated salvoes, to increase the chances to hit and amount of damage done to a target.

Lances are energy weapons of extreme power. Usually mounted in large and heavily armoured turrets, lances use triple or even quad energy projectors to focus its energy into a concentrated beam, capable of burning through even the most armoured hull and cutting smaller vessels in half.

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 plasma reactor which also doubles as its warhead. Once launched, the plasma drive propels the torpedo towards its target, 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 shields - the most shields intercept incoming fire based on its speed. Torpedoes travel slow enough (relatively speaking) that shields will not intercept them and they can pass through these powerful energy barriers unimpeded.

Nova Cannons are huge weapons. 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 Navy vessel is covered with defensive turrets designed specifically to destroy incoming bombers and torpedoes.

Shields are protective energy barriers that allow ships to survive the hostile environment that is 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 fire, forcing the generators to shut down to vent off excess energy.

Every spacefaring vessel is equipped with a certain amount of armour, capable of deflecting impacts on the ships' hull. The strength and thickness of the armour varies depending on the ship'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 ships 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 prow. It is capable of deflecting all but the most powerful of frontal hits.

Propulsion systems
Every Imperial ship is equipped with a plasma drive for normal propulsion through the depths of space. Running up to a third of the ship's length, the aft section is a mass of drive tubes, engine compartments and plasma reactors.

Most Navy ships 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 a warp rift.

The Holy Fleet
Within the literature of the Warhammer 40k universe the Imperial Navy is often referred to as The Holy Fleet. The Ecclesiarchy preach that the fleet is an extension of the Emperor and is therefore holy. This is due to the intimate relationship between the Navigators who are able to guide the fleet though the warp using the beacon emanating from the Golden Throne and the Astronomican. Whether or not the title applies to all vessels in the Imperium is unclear. The Adeptus Mechanicus would also no doubt consider the vessels themselves holy. However, this is due to their own techno-theological beliefs.