Patrol ship

Patrol ships are one of the three primary subdivisions of armed human spacecraft, along with screening ships and capital ships.

Description
Unlike their two peer categories, screening ships and capital ships, patrol ships are largely defined for their unsuitability for fleet work. This relies on the combination of having both the sheer operational endurance to make expeditionary deployments possible, and the ability to attain high movement speeds that is necessary for intense spatial combat. Powerful engines are necessary because it allows a given ship to intercept other warships,. Because most vessels in this group max out at one hundred thousand metric tons in mass, with many struggling to reach a tenth of that figure, it is impossible for most patrol ships to have both of these qualities. Indeed, even those that dismiss a focus on economy still have to make the sacrifice between speed and fuel efficiency, which dictates their specialty. Fast attack craft lacking slipspace drives are normally relegated to system or even interplanetary patrol only, while those capable of interstellar travel and with an eye towards long-duration cruising are largely used for escorting merchants through uninhabited systems.

Cutters
Usually composed of the smallest spacecraft to be considered as starships, cutters are small, lightly-armed law-enforcement ships that are too small to mount slipspace drives. They are restricted to system patrol only, and are thoroughly incapable of engaging any kind of military warship.

Fast attack craft
More of an ad hoc designation than a true classification, fast attack craft are similar in size to cutters, and so lack an onboard slipspace drive. However, they have traded their lighter armaments with oversized weapon systems, which allows them to significantly punch far above their weight. This added mass means that they must sacrifice other elements of their design to retain their speed, such as cargo and hangar bays, active defense systems, and armor.

Fast attack craft are favored by independent human factions that lack an established shipbuilding industry and/or have limited manpower at their disposal, such as insurrectionist cells, small colonial polities, and rogue UNSC units. As a result, most ships manufactured by these parties tend to be poorly built and unreliable, unable to withstand the stresses of battle before breaking apart or being damaged enough to withdraw.

Corvette
Moderate in tonnage for this classification, corvettes are noteworthy for their high cruising speed and addition of a slipspace drive, making them capable of travelling to other systems. However, the size and power consumption of the drive limits their operational endurance, and it is rare to find a corvette that masses less than 20,000 metric tons.

Convoy escort
Convoy escorts invert the usual qualities of patrol ships, instead incorporating a slipspace drive and carrying enough fuel, food, and ammunition to make multi-month-long trips possible. This usually requires a substantial increase in size, and so most convoy escorts trend into tonnages normally found with frigates. Their armament is usually less than that of true warships, primarily done to save costs as the idea is to carry the potential to cause damage to raiding vessels - which their designers hope would deter attacking vessels.

System defence craft
Although patrol ships tend to be among the smaller ships in the human sphere, either by choice or circumstance there are a tiny handful of starships that do technically fall under this classification. System defence craft are effectively warships in every sense of the word, with all the guns, missiles, protection, and even speed afforded to one - but without any regard for slipspace drives and extended operations. As a result, they are unable to leave their home systems, but they make up for this by being incredibly powerful and efficient for their tonnage, as every kilowatt generated by their reactor is directed into their warfighting systems.