Reading the discussion about ship classifications in sci-fi I thought I'd put a little precis on them in the ATL Empire
This listing is only of actual warships in use by the Imperial Navy, not including snubfighters and gunships which are generally considered the property of the Starfighter Corps.
Corvettes - These are the smallest viable 'warships' available, generally intended for picket and screening duties or patrol of rear areas. Typically lightly armed and shielded although several models feature a pair of capital missile launchers in an attempt to remain relevant in fleet engagements. As the ATL Empire is engaged in a war with a peer power, these vessels are increasingly seen as too small and too fragile to be viable platforms and are being phased out of Imperial service. At the same time, system defense forces and the Imperial Customs Service gleefully snap up every single decommissioned Corvette that they can get their hands on, as they are nearly perfect for their needs.
Recently there have been several developments that are somewhat bucking this trend, a series of corvettes designed to be deployed as parasites from larger vessels. Sacrificing range and habitability for increased shielding and weaponry, these vessels are intended to augment interior screens for major fleet units, the fleet trains, etc.
Frigates - A highly variable classification rooted in role rather than size of the vessel. Some Frigates are larger than cruisers, others are almost as small as Corvettes, however they all have an identical role, specifically light escort vessels armed almost exclusively with point defense weaponry and anti-snubfighter armaments. A very small number will carry a very light anti-ship armament, but the current trend is away from such. For their size, these ships tend to possess exceptional sensor arrays as well, making them well-suited as fleet pickets. Several highly specialized vessels also fall into this classification, included dedicated grav-well interdictors, dedicated medical vessels, dedicated electronic-warfare vessels, etc.
A subset of the Frigate classification are the Escort Carriers, administratively listed as such due to the similarities in main armament being limited to point defense and anti-snubfighter arrays. Escort Carriers generally carry up to two squadrons of Imperial X-Wings and are mostly seen in commerce protection roles.
Destroyers - Small, fast, and very heavily armed for their mass at the cost of weak armor and shielding. Imperial destroyers are divided into two general groups, the turbo-laser heavy and the capital-missile heavy designs. They all possess significant point-defense and anti-snub capability, although not nearly as heavy as that found on frigates. Their primary role is as screening units for capital ships and, in squadrons of four to twelve ships, fast attack vessels in their own right coming in behind snub strikes.
Until recently, destroyers were increasingly being replaced by frigates in the screening role as their fragility and small size made it harder to justify them, especially as they began falling further and further behind the line units in terms of sheer firepower. The recent development of ultra-dense hypermatter reactors and innovations in point defense weapon design initially developed for commerce protection (specifically 'strap on' point defense laser turrets that are 100% self-contained with their own small reactor, targeting systems, etc) has mostly saved the category, with several new destroyer designs currently starting mass production.
Light Cruisers - the smallest vessels considered capable of independent patrol duties, albeit only in rear areas. Light cruisers are a somewhat fuzzy designation, with many ships of the classification formerly being classified as heavy cruisers but as sizes have increased across the board they found themselves reclassified. The most distinctive trait of the Light Cruiser is a focus on larger numbers of fast-firing medium and light turbolasers rather than Heavy or Capital grade weapons. A light cruiser firing at full chat is a terrifying sight, especially with the recent development of active cryogenically cooled (as opposed to older coolant systems that relied on non-cryogenic passive cooling) light turbolasers permitting rates of fire previously only thought possible with single-stage boosted 'laser' weapons as opposed to the dual-stage boosted turbolaser.
Light cruisers tend to be the bane of any of the lighter classifications of warships and are extremely in demand as escort vessels in fleet actions, limiting the number available for independent patrol. Certain innovative and aggressive admirals have been known to use light cruisers in hunter-killer packs that have on multiple occasions demonstrated extreme lethality when used in conjunction with destroyer squadrons.
Due to the exponential cost curve of the ultra-dense hypermatter reactors, light cruisers are currently the largest vessels that have benefitted from the new technology.
There are two notable sub-classifications within the light cruiser category.
Light carriers are the smallest 'carrier' that regularly participate in fleet actions, although most are being transitioned to supporting Imperial Marine planetary assaults. Light carriers tend to carry no more than a single group of four squadrons of snubs, and are the lightest carriers regularly fitted to support the Kappa-3 Interceptor (although more and more CVLs are switching to either all X-Wing or mixed X-Wing/Super-Y Mk II loadouts)
Special Operations Cruisers are nominally naval vessels but are specifically tasked with supporting Special Forces missions. These cruisers are among the most expensive ships in the entire fleet, with single vessels regularly costing as much as the largest dreadnoughts in the Navy. No two of them are quite identical, each being bleeding edge for the time it was built and regularly upgraded and modified afterwards. Typically they will possess single-blind cloaking devices, advanced sensors and weaponry, accommodations for multiple special forces units on board with highly sophisticated infiltration and extraction gear, and just about any classified bit of kit imaginable.
Heavy Cruisers - The workhorse of the fleet. The heavy cruiser is possibly the single most common while at the same time the most in demand classification of ships in the Imperial Navy. The ATL version of the classic ISD-II is the ur-example of this category of ships. Heavy Cruisers are not the combination battleship/LHD of the OTL Imperial Star Destroyer. They are the smallest non-carrier vessels to carry snubs, in the ISD-II's two squadrons of Imperial-X's in addition to the utility shuttles found on just about all classes of Imperial ships.
Heavy cruisers are the smallest ships to carry heavy turbolasers and ion cannons, generally supplemented by massive batteries of point-defense and anti-snub armament. Heavy cruisers in fleet service will also carry modular packs of concussion missiles intended for long-range anti-snub and anti-small combatant use, while those on independent patrol replace those packs with additional anti-snub lasers. A few classes of heavy cruiser make use of capital missiles, but the vast majority are 'gun' cruisers focusing on heavy turbolasers for their main offensive punch.
Heavy cruisers are the largest ships ever deployed on independent patrols.
Battleships - The single broadest and most variable classification. All ships within this category share one common trait, they are combat vessels that are intended to be screened by lessor ships, rather than ones intended primarily to serve in the screen. This category is incredibly diverse, with many analysts proposing schemes to differentiate within the category to simplify things.
Battleships range from the ISD-II sized Tector-class, which sacrifices the snub hangars and portions of the anti-snub armament in exchange for massively improved armor protection and more robust shields, to the titanic Assertor-class which are currently the largest warships in the Imperial Navy. There are fast vessels, like the Sword-class. There are general-purpose line units like the Allegiance-class, there are siege units like the Mandator IV's, there are carriers, assault carriers, super-carriers... the listing of sub-categories would almost be a listing of the classes themselves.
Quite literally the only thing 100% in common amongst all 'battleships' is that they will never operate alone. Even the Tector's are never deployed without a screen of frigates or corvettes, and the Assertor's are typically the core of entire capital fleets.
There are two other groups of note. Marine Assault Ships and Auxiliaries.
Marine Assault ships tend to range from destroyer-size to heavy cruiser size and are divided into two rough groups, those intended to land themselves and provide direct support for deployed forces, and those intended to land their Marines using smaller vessels then provide ortillery support.
Auxiliaries comprise 'everything else', from the massive logistics ships that make up the fleet train to personnel transports. If it isn't a front-line combatant it's an auxiliary. At most auxiliaries will be armed for minimal self-defense with point defense and anti-snub weapons. The availability of the strap-on point defense systems have massively increased the protection available to auxiliaries.
This listing is only of actual warships in use by the Imperial Navy, not including snubfighters and gunships which are generally considered the property of the Starfighter Corps.
Corvettes - These are the smallest viable 'warships' available, generally intended for picket and screening duties or patrol of rear areas. Typically lightly armed and shielded although several models feature a pair of capital missile launchers in an attempt to remain relevant in fleet engagements. As the ATL Empire is engaged in a war with a peer power, these vessels are increasingly seen as too small and too fragile to be viable platforms and are being phased out of Imperial service. At the same time, system defense forces and the Imperial Customs Service gleefully snap up every single decommissioned Corvette that they can get their hands on, as they are nearly perfect for their needs.
Recently there have been several developments that are somewhat bucking this trend, a series of corvettes designed to be deployed as parasites from larger vessels. Sacrificing range and habitability for increased shielding and weaponry, these vessels are intended to augment interior screens for major fleet units, the fleet trains, etc.
Frigates - A highly variable classification rooted in role rather than size of the vessel. Some Frigates are larger than cruisers, others are almost as small as Corvettes, however they all have an identical role, specifically light escort vessels armed almost exclusively with point defense weaponry and anti-snubfighter armaments. A very small number will carry a very light anti-ship armament, but the current trend is away from such. For their size, these ships tend to possess exceptional sensor arrays as well, making them well-suited as fleet pickets. Several highly specialized vessels also fall into this classification, included dedicated grav-well interdictors, dedicated medical vessels, dedicated electronic-warfare vessels, etc.
A subset of the Frigate classification are the Escort Carriers, administratively listed as such due to the similarities in main armament being limited to point defense and anti-snubfighter arrays. Escort Carriers generally carry up to two squadrons of Imperial X-Wings and are mostly seen in commerce protection roles.
Destroyers - Small, fast, and very heavily armed for their mass at the cost of weak armor and shielding. Imperial destroyers are divided into two general groups, the turbo-laser heavy and the capital-missile heavy designs. They all possess significant point-defense and anti-snub capability, although not nearly as heavy as that found on frigates. Their primary role is as screening units for capital ships and, in squadrons of four to twelve ships, fast attack vessels in their own right coming in behind snub strikes.
Until recently, destroyers were increasingly being replaced by frigates in the screening role as their fragility and small size made it harder to justify them, especially as they began falling further and further behind the line units in terms of sheer firepower. The recent development of ultra-dense hypermatter reactors and innovations in point defense weapon design initially developed for commerce protection (specifically 'strap on' point defense laser turrets that are 100% self-contained with their own small reactor, targeting systems, etc) has mostly saved the category, with several new destroyer designs currently starting mass production.
Light Cruisers - the smallest vessels considered capable of independent patrol duties, albeit only in rear areas. Light cruisers are a somewhat fuzzy designation, with many ships of the classification formerly being classified as heavy cruisers but as sizes have increased across the board they found themselves reclassified. The most distinctive trait of the Light Cruiser is a focus on larger numbers of fast-firing medium and light turbolasers rather than Heavy or Capital grade weapons. A light cruiser firing at full chat is a terrifying sight, especially with the recent development of active cryogenically cooled (as opposed to older coolant systems that relied on non-cryogenic passive cooling) light turbolasers permitting rates of fire previously only thought possible with single-stage boosted 'laser' weapons as opposed to the dual-stage boosted turbolaser.
Light cruisers tend to be the bane of any of the lighter classifications of warships and are extremely in demand as escort vessels in fleet actions, limiting the number available for independent patrol. Certain innovative and aggressive admirals have been known to use light cruisers in hunter-killer packs that have on multiple occasions demonstrated extreme lethality when used in conjunction with destroyer squadrons.
Due to the exponential cost curve of the ultra-dense hypermatter reactors, light cruisers are currently the largest vessels that have benefitted from the new technology.
There are two notable sub-classifications within the light cruiser category.
Light carriers are the smallest 'carrier' that regularly participate in fleet actions, although most are being transitioned to supporting Imperial Marine planetary assaults. Light carriers tend to carry no more than a single group of four squadrons of snubs, and are the lightest carriers regularly fitted to support the Kappa-3 Interceptor (although more and more CVLs are switching to either all X-Wing or mixed X-Wing/Super-Y Mk II loadouts)
Special Operations Cruisers are nominally naval vessels but are specifically tasked with supporting Special Forces missions. These cruisers are among the most expensive ships in the entire fleet, with single vessels regularly costing as much as the largest dreadnoughts in the Navy. No two of them are quite identical, each being bleeding edge for the time it was built and regularly upgraded and modified afterwards. Typically they will possess single-blind cloaking devices, advanced sensors and weaponry, accommodations for multiple special forces units on board with highly sophisticated infiltration and extraction gear, and just about any classified bit of kit imaginable.
Heavy Cruisers - The workhorse of the fleet. The heavy cruiser is possibly the single most common while at the same time the most in demand classification of ships in the Imperial Navy. The ATL version of the classic ISD-II is the ur-example of this category of ships. Heavy Cruisers are not the combination battleship/LHD of the OTL Imperial Star Destroyer. They are the smallest non-carrier vessels to carry snubs, in the ISD-II's two squadrons of Imperial-X's in addition to the utility shuttles found on just about all classes of Imperial ships.
Heavy cruisers are the smallest ships to carry heavy turbolasers and ion cannons, generally supplemented by massive batteries of point-defense and anti-snub armament. Heavy cruisers in fleet service will also carry modular packs of concussion missiles intended for long-range anti-snub and anti-small combatant use, while those on independent patrol replace those packs with additional anti-snub lasers. A few classes of heavy cruiser make use of capital missiles, but the vast majority are 'gun' cruisers focusing on heavy turbolasers for their main offensive punch.
Heavy cruisers are the largest ships ever deployed on independent patrols.
Battleships - The single broadest and most variable classification. All ships within this category share one common trait, they are combat vessels that are intended to be screened by lessor ships, rather than ones intended primarily to serve in the screen. This category is incredibly diverse, with many analysts proposing schemes to differentiate within the category to simplify things.
Battleships range from the ISD-II sized Tector-class, which sacrifices the snub hangars and portions of the anti-snub armament in exchange for massively improved armor protection and more robust shields, to the titanic Assertor-class which are currently the largest warships in the Imperial Navy. There are fast vessels, like the Sword-class. There are general-purpose line units like the Allegiance-class, there are siege units like the Mandator IV's, there are carriers, assault carriers, super-carriers... the listing of sub-categories would almost be a listing of the classes themselves.
Quite literally the only thing 100% in common amongst all 'battleships' is that they will never operate alone. Even the Tector's are never deployed without a screen of frigates or corvettes, and the Assertor's are typically the core of entire capital fleets.
There are two other groups of note. Marine Assault Ships and Auxiliaries.
Marine Assault ships tend to range from destroyer-size to heavy cruiser size and are divided into two rough groups, those intended to land themselves and provide direct support for deployed forces, and those intended to land their Marines using smaller vessels then provide ortillery support.
Auxiliaries comprise 'everything else', from the massive logistics ships that make up the fleet train to personnel transports. If it isn't a front-line combatant it's an auxiliary. At most auxiliaries will be armed for minimal self-defense with point defense and anti-snub weapons. The availability of the strap-on point defense systems have massively increased the protection available to auxiliaries.