Gunship:
Mass: 500-15,000 tons
Gunships are primarily used by small colonies and warlords in the Terminus or outer edges of Council space. Without the funds to purchase enough larger warships in order to protect themselves these groups buy or make Gunships in order to maximize bang for their buck at a size they can afford. These ships sacrifice things like crew comfort , supplies and sometimes even FTL drives to maximize firepower and maneuverability. Their small size and relatively simple design allows for them to be made on site at small colonies or produced in large numbers on more developed worlds. Gunships are usually produced with a mix of military and civilian grade equipment depending on availability to the faction constructing the vessel, with Gunships made from all civilian grade components not uncommon.
Even the largest and most advanced Gunships have difficulty fighting against military Frigates or even more combat oriented Corvettes, but in large numbers Gunships' design sacrifices that Frigates can't make due to their roles allows for Gunships to take down the larger vessels. Gunships have almost no chance against anything larger then a Frigate in reasonable numbers. Gunships are meant to fight mostly armed civilian ships, other Gunships, or military ships in the hands of pirates who cannot ensure proper maintenance or get the parts to fix the ships to full capability, leveling the playing field significantly.
The most famous Gunships class is the Aslana class. Produced by the Ver'hanva consortium, a terminus corporation, it is about 8,000 tones. The Aslana class has gained notoriety among the council races population as the "Terminus Gunship" due to its prolific use during the Terminus Incursions which were attacks on many Terminus factions after the Morning War due to their increased activity caused by losing the Quarians as a stabilizing factor. After the Incursions the Aslana class has seen many renditions in media, most famously in a popular show in the 2190's to 2200's where a Aslana class ship named the Light of Thessea is upgraded with Prothean technology including particle weapons.
The only significant faction outside the Terminus that uses Gunships in large numbers is the Quarians. They have a large amount of Gunships serving in a multitude of roles but their minimal ability to hold supplies and uncomfortable conditions make them undesirable ships to live in.
Corvette:
Mass: 10,000-20,000 tons
Corvettes are generally ships that specialize in one of the roles of Frigates at the expense of the other roles. This leads to a lack of flexibility but allows for high performance in the role they specialize in.
Scout Corvettes, like the Scout Frigates used by some powers, has a extremely oversized FTL drive, allowing for extreme FTL speeds (up to 15 light years per day) and carry powerful sensors. They usually carry little to no weapons and rely on speed and endurance to survive.
Escort Corvettes have high maneuverability, robust heat storage and radiation system, and a vast network of guardian lasers in order to protect their command ship from fighters, torpedoes, missiles, rockets, and small ships.
Fast Attack Corvettes move at high speeds in order to deliver torpedoes or vast swarms or rockets/missiles to larger ships.
Patrol Corvettes are meant to patrol controlled space and usually have a longer range then any other Corvettes and some of the best sensors (only surpassed by Scout Corvettes).
Most Corvette classes do not have spinal mounted mass accelerators though there are some exceptions.
Frigate:
Mass: 20,000-80,000
Frigates can be said to be the workhorse of most navies. Flexible and large enough to perform most roles acceptably, while being cheap enough to be fielded by most small to mid sized navies and can be fielded in vast numbers by large navies. Frigates perform multiple roles:
Frigates act as picket ships in larger navies, staying far away from the fleet to warn the fleet of any threats and, during battle, creating a sphere of frigates to protect the fleet from torpedoes, missiles, fighters, and small ships with their guardian lasers.
Frigates prowl near enemy fleets, attacking ships with weakened shields in the enemy fleet. They also attack ships with disruptor torpedoes.
Frigates patrol space, fighting pirates and helping damaged ships.
Frigates are used to assault planets, they are small enough for it to be economical and surface area efficient to equip them with the systems to operate effectively on a high gravity world. Some models of frigates are designed to focus on this role and are equipped with large troop bays and weapons more suited for ground support then space combat, these are called Assault Frigates.
Frigates act as scouts for the fleet. It is economical to equip Frigates with oversized drive cores, due to their small sizes. This gives them a high FTL cruse speed, allowing them to outrun pursuers and scout large areas.
Some Frigates in smaller navies are equipped with command facilities due to those navies lack of larger ships. The only major navies to follow this practice is the Salarian navy which has one of the frigates in its patrol flotillas equipped with command facilities in case the flotilla's cruiser is destroyed.
Destroyers
Mass: 80,000 - 250,000 tons
In Council space the destroyer comes from 2 sources, the Turians and the Salarians.
During the Rachni war, the Salarians were running low on materials for ships but needed more warships to fight the Rachni. They began to strip their cruiser designs to stretch resources until the design became little more then a MA and engines. A Asari who visited one of the shipyards producing these ships said "These are not ships, these ships are not meant to travel between the stars, only destroy." And thus these ships were named Destroyers, or the Asari equivalent to the word.
The Turians at first contact already had a class of ships named Destroyers, or their word for it. These ships were a derivative of Frigates that were specialized to destroy larger ships. While Frigate sizes stagnated due to the need to be an economical size, Destroyers continued to grow.
It was quite confusing to everyone that 2 species named 2 ships types of similar sizes the same thing in their own language, this was compounded when the humans made that 3.
The Alliance had 2 types of Destroyers: the first, Light Destroyers were designed around the carronade, a MA designed to launch large projectiles at relatively low speeds. The power of the fire was not in the kinetic energy of the round, but instead from the rounds payload. Acid, Nanits, Nukes, many things can be put into these rounds. Most of the payloads are capable of being created in a omni-forge, something all ships have onboard, allowing the Light Destroyers to reload mid-patrol or even mid-battle, though that is not recommended due to the heat of production.
The second type was the Heavy Destroyer. These ships were created due to the escalating size of Cruisers. At the time Cruisers were the largest straight combat ships produced by the humans and thus were constantly increasing in size. The nations of Earth understood the problem and when the Systems Alliance prepared designs for its first warships, the first class of Heavy Destroyers were part of the lineup alongside, Carriers, Cruisers, Light Destroyers, and Frigates. The type would eventually be redesignated as Light Cruiser due to its differences with the Light Destroyer classes
The type would be revived in order to circumvent the Verge Accord between the Hegemony and the Alliance, mediated by the Asari. The Accord banned weather side from moving any ships of Light Cruiser (over 250,000 tons) class or higher into the Verge. This gave the Hegemony a advantage in there Verge due to the fact that they had a large deniable force under the control the the Alliance, who only started developing one after first contact. To solve this problem by reactivating and modernizing many old Light Cruisers taken out of the deep reserve and redesignation Heavy Destroyers alongside reactivating and modernizing some old Heavy Destroyers. The Light Cruisers were all lighter then 250,000 tons and so were not technically Light Cruisers. This act supplied the Alliance rapidly with a force of relatively powerful ships to protect its colonies without violating the Accords or paying to build undersized Cruisers that would be ineffective in a true war.
Asari Destroyers (luckily not having a name translating to Destroyer) are designed to destroy small ships like Frigates, Corvette, and Gunboats. This is a important role in Asari fleets as it clears the way for the Asar's own small ships to strike at the larger ships of their enemies fleet.
Light Cruiser:
Mass: 250,000 - 500,000
Light Cruisers are the backbone of most large navies and the largest ships of most small navies. They are all equipped with spinally mounted Mass Accelerator cannons going 70-90 % the length of the main hull. These guns are the main weapons used during full battles by large ships.
Cruiser and Dreadnoughts usually have a longer length compared to their height and width compared to Frigates, Destroyers, Carriers, and most civilian ships. This gives them many advantages: they can have a longer MA, giving them more range, they have more surface area to radiate heat, improving combat endurance, and they have a smaller forward cross section, making it harder to hit them. It also comes with some disadvantages that climate how thin they can realistically get: the higher surface area means more mass and volume is sacrificed for armor and outer hull, there is less space at the back of the ship for engines and defenses, leading to lower speed, weaker rear defenses, or both, it is harder to turn the ship without breaking it, and, while it makes it harder to get hit, a hit would breach more compartments and do more damage. Each designer draws the line for how long cruises should be for their tonnage a different points.
Light Cruisers are the smallest type of ship where it is uncommon for ships not to have command facilities, many acting as the flagships of flotillas in large navies and even fleets in smaller navies.
During fleet battles, Light Cruisers are the most common standard combatants, besides Frigates and Destroyers which fill a different role. Light Cruisers have the highest amount of deaths compared to the total number of personnel crewing them due to them being the smallest ship in the battle line, easy pickings for large ships and Destroyer strikes. This make them a disliked post during wartime, amplified by their role as patrol flotilla flagships meaning they are the focus of fire from the enemy during smaller battles.
Heavy Cruiser:
Mass: 500,000- 1,500,000
Heavy Cruisers are the result of a loophole in the Treaty of Farixen. The Treaty originally said that a Dreadnought was a ship that masses 500,000 tons AND had a Mass Accelerator 600 m or longer. This was not a problem during the Treaty's early days as during that time anything even approaching 500,000 tons would be so expensive that it would be more efficient to just build a Dreadnought and be able to have the necessary range to not be destroyed by any dreadnought (at the time the average Cruiser was about 300,000 tons and the average Dreadnought about a million).
At the time of the treaties creation the Turians had 26 Dreadnoughts. The treaty permitted them to have a maximum of 28 Dreadnoughts. At the time of the treaties creation, this number was acceptable as the size of Turians civilization, and the galaxies as a whole, could not support too many military ships.
The Turians were relatively young compared to the other Council species, and the other two species were devastated by the wars. Even with full war time economies, the number of Dreadnoughts fielded by the council during the rebellion never made it to 100 and usually never even made it to 80. By the time of the signing of the treaty, seven years after the war, the number of Dreadnoughts in existence was 63, 26 Turians, 15 Salarian, 16 Asari, and 6 captured Krogan dreadnoughts, the war having dwindled the number.
Each dreadnought is a massive investment of resources that takes years to build, but can annihilate entire small fleets. The average Turians Dreadnought is 8 times the mass of its Cruiser contemporary, but has 4 time the shield strength, 8 time the shield regeneration, twice the range, and the firepower to break a Cruisers shields in one shot. It would take 8 Cruisers constantly hitting a Dreadnought for 2.73 seconds to break its shield (2.42 mt per shot, one shot per 3 seconds per ship, 4 mt shield regeneration with a 20 mt shield strength for FCW Cruisers and Dreadnoughts) and in space battles all shots do not hit. Their only real weakness compared to Cruisers is that they cannot radiate heat as well so they have limited endurance.
As time went on, however, the dreadnought number restriction created by the treaty became a problem and the Turians began looking for a workaround. The civilizations increased drastically in size and so they could field larger navies with more and bigger ships. Cruiser designs began to appear that reached near the limit and some surpassing it. The Turians wanted a ship class large enough to beat any of these Cruisers while not being limited by the treaty so they started looking for loopholes, and found one. In 1844 the first Heavy Cruiser began construction with countless of it brethren. By the time the Asari could start trying to force amendments to the treaty decades there were over 100 Turians Heavy Cruisers and many other from different species. The concept actually took hold the most in the smaller Asari Republic Navies. The rights to the 18 Dreadnoughts the Asari could have were auctioned off not long after the treaty was signed, some were not even used, purchased to restrict the military might of other Republics. Many Republics did not have rights to these slot but wanted a competitive force, and the costs even suggested for the purchase of one of the slots were crippling. The Heavy Cruiser gave those Republics a opportunity to have ships larger then Cruisers, some even rivaling Dreadnoughts in mass. Eventually a compromise was reached, Heavy Cruisers would be added to the Treaty as a separate ship type, 500,000-1,500,000 tone with 500-650 m mass Accelerators. They would not be restricted in number, but private interests like PMCs are not allowed to have them.
There are 2 types of Heavy Cruisers design philosophes, the upscaled Light Cruiser and the Pocket Dreadnought. The Turians design their Heavy Cruisers based on their Light Cruisers, only 2 spinal mounted MA, but long range, they act as command ships for patrol fleets and lesser capital ships in numbered fleets. Pocket Dreadnoughts are designed to be as close to Dreadnoughts as possible without violating the treaty. This type is primarily used by Asari Republics as everyone else either they don't need them (Turians, Salarians,), can't afford to fill up all their Dreadnought slots so it is better to build Dreadnoughts instead (Elcor, Hannar, Batarians), don't need them (Volus) or are not restricted by the treaty.
Dreadnought:
Mass: 1,500,000
The arbiters of space warfare, Dreadnoughts are capable of taking on small fleets on their own. Only the largest powers can afford to field more then a handful of Dreadnoughts. The Treaty of Farixen originally restricted the number of Dreadnoughts each species could have, 28 for the Turians, 15 for the other Council races, and 5 for the Associate races. This changed after the Morning War. In order to protect the galaxy from the Geth and the resurgent Terminus Systems, the Treaty was revised to allow the Turians to build 36 Dreadnoughts, the Council races 24, and the Associates 8.
At the time of first contact the Citadel races have 80 Dreadnoughts in full operation, 36 Turians, 24 Asari, 15 Salarian, 6 Batarian, 4 Va'ne'ru'go and 1 Elcor.
The Turians and Asari have use all of their slots for Dreadnoughts but the Salarians do not have the will or the economic strength to operate all of the Dreadnoughts they could, 9 older Dreadnoughts are kept in reserve, their military's funding not allowing them to be kept in full operation, but they could be brought online in only a few weeks.
After a major Terminus campaign ravaged their space a movement for a higher militarization began in the Elcor population, which lead to the construction of their one Dreadnought, the Pride of Dekuuna, and several other ships. Some believed this would lead to the Elcor becoming a more significant power and becoming the only Associate race in centuries to fill all of their Dreadnought slots (the Quarians were the last species to have that title, with all 5 of the Dreadnoughts they were allowed at the time being in operation), but the movement was quietly killed in its crib by other governments, leaving the Pride of Dekuuna as the only Elcor Dreadnought, and several decades out of date by the time of the FCW.
The Batarians have been expanding their military since their contact with the Citadel races. At the time of first contact 80 years before the FCW the Hegemony fleet had no ships larger then a Light Cruiser. As of the the FCW the Hegemony fleet has 6 active Dreadnoughts with their first 2 Dreadnoughts, Glory and Triumphant, in reserve. The Hegemony had built another Glory class Dreadnought, the Champion, but it was damaged beyond repair during the first war with the Narn 45 years before the FCW, and had to scraped. All of the Victorious and the Khamen Grascerrok classes, 3 of each, are still in operation.
The Va'ne'ru'go, being mostly surrounded by the Terminus Systems, is very militarized, but has a relatively weak economy. The Va'ne'ru'go's government can only afford to operate 4 Dreadnoughts. One Dreadnought is deployed with each of their fleets. The first fleet protects their homeworld, the second fleet protects the rest of their systems, the third fleet protects the Burning Sky cluster relay, and the fourth fleet operates as a independent force and commonly participates in joint actions with Turian fleets, usually the 10th fleet.
Many Terminus powers have Dreadnoughts with all of the powers combined having 59 active Dreadnoughts.
Carriers:
Mass: Variable
When humanity came onto the galactic stage, they brought with them a new idea, Carriers. Carriers are meant to carry and deploy drones, probes, and Fighters on an unprecedented scale.
Carriers come in 4 sizes: Patrol, Light, Heavy, and Super.
Patrol Carriers are small, Frigate mass or less, vessels that are not meant to be used more as a police ship then a warship, deploying a small number of probes and satellites in orbit of a newly colonized planet to act as a temporary communication and early warning system for the colony until a permanent system is established. Then the ship would pack up its equipment and leave for the next colony.
Light Carriers are fleet units around the mass of Light Cruisers that are the most common Carriers in Alliance space. Light Carriers are attached to combat formations in order to supplement the other ships in the formation's small craft.
Heavy Carriers are the largest Carriers produced before or during the FCW, about the mass of a Heavy Cruiser. 2 Heavy Carriers are the center of Alliance Carrier Groups with 12 Frigate escorts. Each fleet has 2 Carrier Groups with a total of 4 Heavy Carriers per fleet.
Supercarriers are a design proposed for a Carrier with a mass equal to the Everest class Dreadnought. It would have thousands of Fighters and tens of thousands of drone with the ability to control the space in a entire system. The class was proposed for funding by the military but was rejected by parliament, claiming it is "unnecessary for the defense of the Alliance and a waste of resources that could be used better elsewhere".
Assault Carriers are Light Carrier massed vessels controlled by the Systems Alliance Marine Corp which is designed to invaded planets. Only 5 of these vessels exist.