So, in today’s piece of worldbuilding, have an analysis and explication of the different classes – or the different types, rather – of military starships operated by the Imperial Navy. (The basis for the ternary plot I’m using is, of course, Winchell Chung’s analysis here, so you might want to go read that first if you’re not familiar with the concept, then come back here.)
The chart on the right illustrates the differences between the various types and classes of warship in common use by the Imperial Navy by their P/D/W ratio – i.e., the relative trade-off between propulsion, defenses, and weapons (i.e. offensive armament):
“in common use” should be read as “not counting all the weird-ass specialist ships we build for special cases”; also, it doesn’t include auxiliary vessels (oilers, hospital ships, etc.) since they’re not operated by the IN, but by the Stratarchy of Military Support and Logistics.
Battleships, Dreadnoughts and Superdreadnoughts
“I am an Imperial Mandate-class dreadnought, and you are within a million miles of me. Ergo, you continue to exist solely on my sufferance.”
– an early experiment in AI captaincy
Battleships, dreadnoughts, and superdreadnoughts (B, D, S on the chart) are capital or supercapital ships mounting heavy long-range firepower as their primary function.
These types, the ships of the wall, are the kings of the outer engagement envelope, engaging each other with powerful weaponry at ranges of up to two light-minutes, and rarely closing beyond one to two light-seconds range (a zero/zero intercept at this residual range is considered a “set-piece” battle). They are the purest of all naval vessels in function, existing simply to counteract each other in the battlespace of major fleet actions, or to own the volume of space they can dominate if not opposed; the ultimate argument of star navies.
The principal difference between two of the three types is simply mass and volume; doctrinally, the majority of the ships of the wall of any given time should be of battleship classes, with their larger cousins the dreadnoughts providing heavier stiffening formations to the wall and occasional nasty surprises.
Because while it sure would be nice to build nothing except dreadnoughts, even nearly-post-scarcity economics doesn’t stretch to overbuilding everything just in case.
Superdreadnoughts, while sometimes referring to particularly large dreadnought classes, more typically refer to ships falling in the dreadnought type by mass, while using much of their internal volume for specialized systems: typical examples would include the command superdreadnought, the information-warfare superdreadnought, the anti-RKV superdreadnought, and so forth.
One example of this listed separately (L on the chart) since its P/D/W ratio moves it well outside the standard range is the mauler superdreadnought. In this case, the specialized systems in question are a very, very large mass driver or laser, with propulsion and defensive systems stripped back to accommodate it.
Mauler superdreadnoughts are not considered ships of the wall, but rather are specialized vessels used to attack specific hardened targets. Since their low speed and weak defenses render them vulnerable “glass cannons”, they are typically operated as part of a task force including close-in point-defense cruisers, and only brought up once opposing fleets and mobile defenses have been cleared away; however, in their specialty role of cracking hardened fixed bases, they’re unequalled.
The “hyperdreadnought” is a peculiarly unique version of the superdreadnought type, of which the Empire fields three, each unique within its class; Invictus, Imperiatrix, and God of War. In order, they are the home of Admiralty Grand Fleet Operations, the Imperial Couple’s personal flagship, and the literal embodiment of the archai/eikone of war. Any one of them turning up in the battlespace would have implications that, by and large, no-one wants to think about thinking about.
Battlecruisers and Cruisers
The backbone of the fleet, battlecruisers and cruisers (C on the chart) are middle-weight combatants, more heavily armed than destroyers and frigates, and yet more maneuverable than battleships and larger ships of the wall. Most cruisers also maintain limited AKV facilities. They are perhaps the best balanced (between operational aspects) of any of the Imperial Navy’s standard types. The distinction between cruisers and battlecruisers is simply one of mass and volume, with battlecruisers identifying the significantly larger and heavier classes of the type.
In fleet operations, battlecruisers and cruisers serve as screening elements and operate on the fringes of the close-in battlespace, maneuvering aggressively for advantage. For the most part, however, these middle-weight combatant types are intended for patrol operations and long-endurance “space control” missions, sometimes alone and sometimes in flotillas, as well as serving as the IN’s go-to types for independent missions of almost any type. In areas of heavy patrol activity, cruisers may lead destroyer or frigate flotillas into action.
Cruisers are also the type within which most variation exists, and cruiser classes may wander quite far from the indicated P/D/W ratio. Of particular note here is the point-defense cruiser (“pd” on the chart), the one type which you might see as a ship-of-the-formation, stripped of most of its offensive armament in exchange for point-defense enhanced to the point of augmenting that of other ships, but many other specialized varieties exist: the assault cruiser (optimized for planetary assaults, i.e., heavy on the ship’s troops and capable of launching drop shuttles and drop pods into atmosphere; some of these are aerospace cruisers, which atmospheric interceptors can sortie from before there’s an orbithead established); the diplomatic cruiser (a big stick to transport the softly-speaking); and the interdictor cruiser (specializing in the volume-security mission, which is to say, to chase down, capture and board other starships). The primary battlecruiser variants are the command battlecruiser (optimized to carry the admiral commanding a CC/BC task force) and the carrier-battlecruiser (which carries AKVs – see below – as well as its internal armament; this is the type of battlecruiser usually found operating alone, due to its significantly enhanced operational envelope and capabilities).
Due to their versatility, the IN maintains a greater tonnage of battlecruisers and cruisers in commission than starships of any other types.
Destroyers and Frigates
Destroyers and frigates (D, F on the chart) are small, fast, maneuverable ships used for screening larger vessels, as escorts, and for patrol work. On their own, their capacity is severely limited, for which reason they typically operate in flotillas assigned together.
As with the above two types, the most obvious difference between destroyers and frigates is their mass and volume. That said, the strict difference between these two types is that while a destroyer may possess very limited broadside armament, due to its limited volume, it does possess it. A frigate, however, possesses no broadside armament; its spaceframe is essentially constructed around its primary gun.
Like cruisers, destroyers and frigates are designed for the “close-in” battlespace – with the understanding that close-in, in space terms, means anything under one light-second of separation. Indeed, these types arguably dominate this battlespace, since they form the majority of the IN’s screening forces, whereas cruisers are largely incidental to “set-piece” naval engagements. In this area, they use their superior maneuverability to both engage each other with wolf-pack tactics and to swarm larger ships at close-in range. Their lesser defensive capabilities than their larger cousins reflects the intention that they should substitute speed and maneuverability, avoiding being hit, for the ability to withstand taking one.
Destroyers and frigates are also intended to serve in escort and patrol roles in relatively safe space, where antipiracy patrol is the main concern (a flotilla of destroyers or frigates is considered an effective counter to a single cruiser-class vessel, which would be a rare high-end encounter under such circumstances); and in small numbers and specialist classes as scouts, avoiding engagement entirely.
Some frigate classes, uniquely among naval vessels, are capable of atmospheric entry and landing. Such frigates occasionally serve an additional role with Imperial Naval Intelligence.
Autonomous Kill Vehicles (AKVs)
AKVs (A on the chart) – autonomous kill vehicles – are extremely smart multi-bus, multi-munition, multi-mission missiles. An AKV is, in effect, a small, stripped-down, AI-piloted starship – capable of much higher acceleration and greater maneuverability than a standard design, albeit with much less endurance – designed to act in multiple roles: as a mobile reconnaissance platform; as a “fighter craft” used to swarm and destroy larger starships from inside their own point-defense zones; or, when it loses all other fighting ability, as a kinetic energy weapon in its own right.
As indicated on the chart, AKVs have essentially no defensive weapons of their own; the intent is that they should substitute their vast advantage in speed and maneuverability for armor and point-defense.
A monitor (M on the chart), in essence, is a fixed base – an orbiting station or asteroid base – used for local defense. Their W/D ratio is skewed more towards defense than the ship-of-the-wall types, since unlike those, they lack even minimal maneuverability to avoid incoming fire or to retreat from the battlespace; on the other hand, their lack of concern for acceleration or other propulsive matters means that there is effectively no upper limit on the mass of the weapons or defenses that a monitor can mount, and asteroid-based monitors may make extensive use of the asteroid’s mass as armor and heatsink both.
Carriers (V on the chart) are battleship or dreadnought-sized vessels which eschew armament of their own in exchange for carrying a large number of AKVs, along with AKV replenishment supplies, strap-on AKV thruster packs, observation platforms, etc. Since they are not generally maneuverable enough or well enough protected (the massive flight deck of a carrier is essentially a corridor through the armor into the heart of the vessel) to survive heavy attack, they are usually held back from engagements, and as such their designs heavily emphasize point- and local-space defense over additional propulsion.
Assault carriers – i.e., those carrying dropships rather than AKVs – also fall into this category. The same general operational rules apply; they are held well back from any engagements, and do not move in to the target area until the high orbitals have already been cleared of the enemy.
Starfighters / Scouts
Starfighters (“sf” on the chart) are not manned fighter-class vessels. (The intersecting rules of physics, economics, and tactical effectiveness do not, in the general case, support a fighter-class of spacecraft in direct analogy to fighter aircraft. Rather, such craft can be replaced trivially by an equivalent vessel removing the biosapient pilot, their life support, and the ensuing limitations on maneuverability, acceleration, and computational performance, and replacing them with a computronium block; in effect, converting the spacecraft into an unmanned AKV.)
Rather, starfighters and scouts are essentially mini-carriers, suitable for operation by a very small crew, or even on occasion a single sophont, dedicated to the special operations and reconnaissance roles. They are small, no-frills starships designed to carry a limited, but still useful, number of AKVs or observation probes in exterior clamps. On arrival at their target, the AKVs or probes are then released to carry out the mission, while the starfighter itself serves as a command post, repair and replenishment depot, and coordination node in the tactical ‘mesh.
Couriers (“o” on the chart) are simply militarized (in construction standard) versions of the equivalent civilian type. While remaining, for the most part, “all engine”, military couriers add limited defensive and extremely limited offensive capability to give them at least minimal survivability in the event that they must pass through an engagement envelope; doctrine, on the other hand, demands that couriers should avoid engagement at all costs utilizing their superior acceleration and maneuverability to any other warship type.