UNSC Navy

The UNSC Navy (UNSCN) is a human naval force, and one of four military branches of the UNSC. It is responsible for all naval operations in space, including but not limited to: interstellar transportation, ship-to-ship combat, deep-space law enforcement and expeditionary operations. Along with the UNSC Marine Corps and elements of the Aerospace Force, its field units fall under the authority of the unified Naval Command.

The Navy was birthed in response to the widespread violence that predated the Interplanetary Wars, and quickly grew due to the influx of assets and personnel belonging to the defunct United Nations Colonial Peacekeeping Force and various international armed forces. At first, riots and unrest in the Sol system meant that they remained largely confined to the region for the first two centuries of existence. Throughout the twenty-fifth century, they expanded rapidly to become the largest human-dominated naval force in history, thanks to successful attempts at usurping the existing Colonial Navy. They played a major role in both the Inner Colony Wars and the Insurrection, where they enforced sanctions on rebelling colonies, transported counter-insurgency units to trouble-spots, and delegated ships to protecting and searching civilian vessels. The UNSC Navy was authorized to take control of all naval assets and personnel at the beginning of the Human-Covenant War. In spite of this, they took horrendous losses at the hands of the Covenant; even with replacements, their fleet dropped from 2,034 ships to only 489 slipspace-capable warships at the conflict's conclusion.

Mission
Broadly speaking, the purpose of the UNSC Navy is to build and sustain a spacefaring naval force that can be used to promptly and efficiently wage war in space, using its fleet of large warships to further the interests of the UNSC itself. This primary mission involves maintaining UNSC presence in both inhabited and non-inhabited systems, in contrast to the UNSC Aerospace Force, whose responsibilities are concentrated around the colonies. To achieve this, they are obliged to train personnel to maintain and operate both warships and naval aviation arms, and must continue to evolve their understanding of naval theory, technology, and organization.

The UNSC Navy is also obliged to fulfil a number of supplemental missions, including but not limited to:
 * General transportation across space (spacelift)
 * Projecting UNSC influence across space (power projection)
 * Uncontested control of space and low-orbit regions (space control)
 * Search-and-rescue of both UNSC personnel and civilians in space.

Field formations
The UNSC Navy's organization for its starships has evolved and changed several times over the course of its lifespan, with the most modern iteration prioritizing easy reassignment of units and autonomy among its local headquarters spread throughout human space. Their naval forces are broadly divided into two main groups of formations, colloquially known as 'temporary' and 'permanent' forces. Temporary forces are custom-built for the needs of a single goal, and are immediately disbanded upon its completion. Permanent units are more general-purpose assignments whose duties are often locked within operational regions. They are only 'deactivated' when either their spacecraft are unavailable for assignment, moved to new commands, or are deemed impossible to practically support them in the foreseeable future. This does not always correspond to when moving ships are placed into temporary formations; squadrons assigned to task forces still retain their individual name and setup.

Regional fleets
Regional Fleets are the largest permanent formation of warships available to the UNSC Navy, whose mission is to defend one of the UNSC's headquarters systems, one for each FLEETCOM Sector and one for SolCore. They are commanded by either an Admiral or Fleet Admiral, who also is part of the local Central Command's leadership, and are generally composed of no fewer than 150 ships each. These ships are subdivided into two Numbered Fleets and a number of 'orphaned' squadrons and flotillas that are directly organized under it. Because of their vital objective, they have the power to requisition and fold any starship or fleet unit under their direct control without any prior approval, provided that they have are operating within the same sector. This power means that in theory, a Regional Fleet can consolidate and deploy thousands of ships in a single engagement, although the challenges in directing an armada of this size has prevented its practical use. While a necessary part of defensive plans, Regional Fleets see very little service outside of a handful of patrols into nearby regions that directly neighbor the system they are home-ported in. As a result, it is not uncommon for a considerable amount of ships to be detached into temporary Battle Groups, which are returned upon completion of their assignment.

Only five Regional Fleets have ever existed at any one time. Unlike smaller fleets and groups, they are not numbered, but they are named after the system they are home-ported in, with the exception of the Sol-based Home Fleet.
 * Home Fleet: Assigned to SolCore; currently active.
 * Epsilon Eridani Fleet: Assigned to FLEETCOM Sector One; currently active.
 * Ectanus 45 Fleet: Assigned to FLEETCOM Sector Two; destroyed during the Siege of Chi Rho.
 * Cygnus Fleet: Assigned to FLEETCOM Sector Three; destroyed during the Siege of Paris IV.
 * Bhaakto Fleet: Assigned to FLEETCOM Sector Four; destroyed during the Siege of Alluvion.
 * Delta Pavonis Fleet: Assigned to FLEETCOM Sector 2; currently active, replaced the Ectanus 45 Fleet.
 * Beta Comae Berenices Fleet: Assigned to FLEETCOM Sector 3; currently active, replaced the Cygnus Fleet.

Numbered fleets
Numbered Fleets are large naval formations that are made of between 50-90 ships, which are organized into four or five Groups and a handful of Squadrons and Flotillas for further support. They are commanded by Vice Admiral, and are intended as an autonomous, multipurpose force that could undertake a number of objectives over a reasonably broad region of space. Their leadership structure is designed to operate completely independently without any orders for extended periods of time, and their field endurance is also similarly improved over smaller units thanks to an integrated logistics division. As a result, Numbered Fleets are most often called upon to conduct major expeditionary campaigns away from their home ports, and may be temporarily reassigned to hub colonies for the duration of a given mission.

Unlike in smaller Groups or Squadrons, the sheer numbers of ships, fighters, and personnel assigned to Numbered Fleets makes it impossible to coordinate them under a single bureaucratic layer. The fleet's command staff therefore disseminate their orders below into a number of subordinate divisions. These are typically organized into commands for conventional naval forces, logistics, aviation arms, and intelligence, with the UNSC Marine Corps also being briefed here due to their close working relationship. Through these, the Admiral can identify and issue necessary instructions to various parts of the fleet, focusing on the larger strategic picture while lower divisions plan the actual tactical micro-management that needs to take place. Multiple departments can work together to create cross-command units with the same orders, thanks to a unified rank structure and shared policies. This is out of sheer necessity, as subordinate units can only be detached away from the main fleet for a limited amount of time without support.

The most common configuration of Numbered Fleets is made up of three Carrier Strike Groups, one Assault Group, and one Logistics Group at their core, which is then supported by one standard Flotilla and one Cruiser Squadron. However, the ease in which Numbered Fleets can be tweaked allows for any combination of Groups, Squadrons, or Flotillas to be pulled together based on regional need.