A Mark 33 Spitfire naval coilgun battery mounted on a Autumn-class cruiser.

A naval coilgun is a type of weapon system that is most widely used by the UNSC Navy.

Description

Naval coilguns are a large, diverse group of armaments, ranging from relatively light dual-purpose cannons, to station-mounted superweapons measuring kilometers in length. All are designed for use against enemy warships, accelerating their shells through the use of dense electromagnetic coils that run the length of their barrels. Their shells are usually heavy slugs made out of tungsten or depleted uranium, and deal damage by concentrating kinetic energy within as small an area as possible. Weight and size constraints of the shell prevents naval coilguns from having the same range and guiding qualities of missiles, so outside of spinal cannons and battleship batteries, they are limited to short and medium ranges. To make up for this, their higher initial velocities and more solidly-built munitions means that regular countermeasures used for deterring missiles do not work on these weapons. Because of power constraints, most models fire in at a slow, steady pace.

Because of their size and expense, naval coilguns can be mixed-and-matched with various turret mounts, with most being twin arrangements. These turrets were generally unmanned, and are instead coordinated via a sophisticated targeting computer that received orders from the battery commander or fire control officer on the bridge. A manual control station may be included on some models as a backup.

Naval coilguns can utilize a wide range of shells, although kinetic kill vehicles and semi-guided shells are the most common. Other options may include nuclear warheads.

Naval autocannon

A somewhat more specialized category, naval autocannons distinguish themselves from other coilguns by their much faster rate-of-fire. This is usually accomplished by using a combination of smaller shells, alternating coilguns, and a substantial electrical storage bank. They are generally used as part of a ship's tertiary battery, where most act as a deterrent against both fighters and swift attack vessels. Although they can fire at a steady rate, they usually fire in blitzing salvos to improve their performance against energy shielding.

History

Railguns and weapons that utilize electromagnets are a concept that dates back to before humanity's first solar colonies were established, although until the 24th century, they were never fully adopted outside of test models. The technology simply wasn't matured to the point to be viable, and the lack of opponents with any forms of armor meant that neither the UNSC nor their CMA counterparts bothered pursuing the concepts. Instead, innovations were tested and funded in the private sector, where surface-to-orbit mass drivers were incrementally improved over the centuries. It was not until the Inner Colony Wars that they fully replaced electrothermal naval guns, though they still remained a rare sight on warships.

The onset of the UNSC-CMA Cold War of the late-2400s saw the technology being matured further.

Models

Naval coilguns

Name	Manufacturer	Build range	Caliber	Maximum firerate	Description
Mark 6 Armstrong	Armstrong Munitions Inc.	2486 - 2518	180mm (7")/45 cal	42 RPM	The smallest naval coilgun to be accepted into service, the Mark 6 Armstrong was normally equipped on patrol ships and freighters to protect them from pirates and large asteroids. It was one of the few weapons of its type to be truly dual-purpose in nature; it was light enough to be installed on fast-tracking turrets to destroy space fighters, and had the punch to comfortably threaten small frigates and destroyers. However, it was underpowered and was slow to fire for a weapon of its size and caliber, and by the 2510s warships had thick enough armor to resist Armstrong cannons. Because of this, they were being phased out of service by the beginning of the Human-Covenant War, either being sold or redeployed to planetary assignments. Armstrong coilguns were originally installed in single-mounts, but twin or even quad turrets were not-unknown by the 2510s.
M112 Viper	Dunkirk & Omdahl	2504 - 2538	375mm (14.7")/34 cal	40 RPM	The M112 Viper was a capable weapon system that was devoted solely to ship-to-ship combat, and often formed a formidable primary battery on the CMA's frigates and destroyers, and in a secondary position on their capital ships. With a barrel length of over 10 meters, it has a high cycling rate for a coilgun, made possible thanks to the use of high-quality capacitors. The Viper would pound on the hulls of enemy escorts to batter them into submission, once they entered its conservative range. Although it was initially offered in a twin turret, later advancements in reactor technology allowed them to be installed in the formidable quad 11A2R1 battery, which fired in a synchronous fashion to improve the Viper's ability to penetrate armor.
Mark 55 Castor	Misriah Armory	2553 - 2570	400mm (15.7")/30 cal	26-35 RPM	The Mark 55 Castor medium naval coilgun was an ingenious weapon system that was perfectly tailored to the different warfighting environment that the UNSC found itself in after the Human-Covenant War. Popular on frigates and destroyers, it combined a rather-heavy projectile with intelligent fire control software that could dynamically alter the gun's performance to specialize it into an anti-armor and anti-shield role. It initially suffered from a number of issues; it was originally only available in a propriety single-gun turret (one that could be paired with two Mark 57 Arena PDGs), the ammunition was prohibitively expensive due to the inclusion of shield-bypassing shells, and the turret itself had a number of reliability issues. Misriah Armory's support and constant refinement eventually solved all these problems, helping it become one of the most numerous naval guns in the UNSC Navy by 2565.
Mark 2488 Onager	Misriah Armory	2488 - 2494, 2539 - 2552	150mm (5.9")/185 cal	20 RPM	Derived from one of the CMA's early attempts to fabricate MACs for patrol ships and destroyers, the Mark 2488 Onager was a rather powerful weapon that was created specifically for long-ranged attack. Using a miniaturized, hyperdense shell crafted from tungsten and depleted uranium, it could easily penetrate the armor of light capital ships and inflict significant structural damage against smaller targets. Because of its high power requirements, and the cost of building it and its heavy-duty turret, Onagers were only mounted on battleships and carriers.
Mark 33 Spitfire	Weapon System Technologies	2522 - 2552	647mm (25.4")/40 cal	6-15 RPM	Considered unnecessary before the Human-Covenant War broke out, the Mark 33 Spitfire quickly grew to become the most popular heavy naval coilgun system used in the UNSC. Mass-produced once it became clear that magnetic weapons were most effective against energy shielding, the Mark 33 Spitfire was well-balanced between cost-effectiveness, reliability, and firepower, and was devastating against escorts while still being effective against capital ships. However, its mass limited its use to vessels and installations heavier than cruisers, and its slow rate of fire was considered its greatest drawback. As a result, its manufacturer constantly tweaked the design and released regular upgrade kits to rectify these problems. Spitfires were first offered in single mounts, but they were most commonly installed an upscaled version of the twin Mark XVII turret. It also popularized the 647mm shell; at the war's beginning, these only had the standard kinetic kill-vehicle and guided shells. By its end, dozens of exotic shell types were built for this caliber in order to improve the effectiveness of these weapons.
Mark 40 Spitfire	Weapon System Technologies	2554 - onwards	700mm (27.6")/35 cal	10 RPM	Developed for the Autumn-class cruisers, and intended for use against enemy cruisers and carriers, the Mark 40 Spitfire piggy-backed off the various upgrades made to the preceding model in order to emerge as a highly-refined weapon system. Improvements in materials made these lighter, much simpler to build, and more efficient. Upgraded electromagnetic coils and use of the heavier 700mm shell made it much more capable of defeating enemy shields and armor, and extending the distance it was effective at. Although its subpar cycling rate was considered disappointing, and the new caliber does not yet have the diversity nor abundance to be truly useful, Weapon System Technologies had somewhat addressed this by adding compatibility for a number of legacy shell types. The capability of the new Spitfires was one of the biggest contributors that led to a significant closing of the gap between human and Covenant warships, and would be a benchmark that all future coilguns were measured against. Like their predecessors, the Mark 40 Spitfire was most abundant in twin turrets. Later in its lifespan, triple turrets would become an option as well.
Mark 15 Breakwater	Weapon System Technologies	2518 - 2552	1,270mm (50")/65 cal	0.5 RPM	The heaviest of the UNSC Navy's line of general-production turreted weapons, Breakwaters could only be used as the main battery on battleships and heavy carriers, where they would strike out at long range and cripple the protection of enemy supercapitals. Despite this, their basic design was surprisingly simple, simply being a corvette MAC which had been rechambered for 1,270mm ammunition. The issues with their size and weight were further complicated by their extremely low rate of fire, which required them to be installed in turrets that could accommodate multiple Breakwaters to make up for this. Breakwaters were found in purpose-built twin, triple and quad turret configurations. In the post-war era, after production had ceased, a new quint turret was unveiled to further concentrate the salvos these monster weapons could dish out.

Naval autocannons

Name	Build range	Caliber	Maximum firerate	Description
M66 Sentry	Weapon System Technologies	2504 - 2552	279mm (11")/36 cal	360 RPM (in short bursts)	Since its introduction in 2504, the M66 Sentry has become the single-most successful naval gun in history, and was mounted on everything from corvettes and patrol craft all the way up to battleships and battlestations. It was an excellent heavy anti-air gun and light anti-ship weapon, partially because of its rapid-firing salvos and high velocity of its rounds. Even the heaviest of space fighters could be annihilated by a single hit, while it still represented a threat to smaller warships, although its viability against anything heavier than frigates was questionable. Although Sentries were optimized for twin-turret configuration, where each coilgun alternates to maintain a steady stream of fire in salvos, there were single and later triple and quad turrets developed for them.
M74 Sentry	Weapon System Technologies	2546 - 2570	330mm (13")/34 cal	400 RPM
M40 Cascade	Weapon System Technologies	2517 - 2552	400mm (15.7")/40 cal	260 RPM
M93 Torrent	Misriah Armory	2543 - 2570	508mm (20")/32 cal	180 RPM