The Citadel races have classified the known variants of Reapers into four types:
CAPITAL SHIPS are Sovereign-class Reapers two kilometers in length. They typically target the dreadnoughts, defense installations, and industrial cities of organic civilizations. Experts believe the Reapers harvest a single species of organics during each cycle of extinction to create these massive ships. Some capital ships are capable of launching small drones equivalent to fighters.
DESTROYERS are 160 meters long and, in astounding numbers, make up the bulk of the Reaper fleet. They engage cruisers and other, smaller ships, as well as communications posts and enemy command centers. Research suggests destroyers are created from those species not harvested to make capital ships.
TROOP TRANSPORTS carry husks to unconquered planets and bring victims of the harvest to Reaper processing centers. They vary in length from 200 meters to one kilometer, but, unlike capital ships and destroyers, do not appear to be self-aware. Instead, other Reapers operate troop transports remotely.
PROCESSORS, also called "slaughter ships," are mobile centers for mass DNA harvesting. Like troop transports, processors appear to be remotely operated by sapient Reapers.