An ancient design dating back to the Great Crusade the Chainsaw class was originally intended to escort convoys that were suffering heavy losses to raiders who were using bombers and interceptors to cripple ships before moving in to board them. The vessels and the attack craft groups they carried proved so effective that they soon found themselves on the frontlines of the crusade. They played key roles in many Imperial victories but unfortunately for the Imperium most of these vessels joined the forces of Chaos during the Horus Heresy with the bulk of the loyalist Chainsaws being lost in the conflict. Even worse much of the information regarding the design, including blueprints and even the location of the forgeworld where most of the class had been constructed, was lost.
In year 857 of M34 the last Chainsaw class vessel in the Imperial Navy was retired. For thousands of years Chainsaws were only seen as part of Chaos War Fleets. But Chainsaw class Vessels began appearing in a number of pirate fleets in mid M41. Some Imperial strategists believe that an outlaw group or a pirate lord salvaged the vessels from ancient battlegrounds but others fear that the forgeworld which built the vessels may have been rediscovered and is now aligned with a band of renegades.
The Chainsaw class is large for an escort but its advanced drives allow it to match acceleration with smaller vessels. A dorsal mounted laser battery provides close quarters firepower, covering the forward, port, and starboard arcs, while a standard frigate turret array provides point defense. For long range power the class carries a pair of primary launch bays. In Imperial service it was typical for one bay to carry Interceptors while the second carried Bombers while many Chaos vessels have replaced the Bombers with Assault Boats. Some of the known pirate Chainsaws carry the typical wing of anything the pirates can make fly others carry groups of attack craft of unknown origin lending support to the idea that pirate Chainsaws are being constructed rather than salvaged and rebuilt. In addition to the main bays the belly of the design has smaller bays typically equipped with a single fighter craft.