The Acheron was a space pirate flagship.
Built five years prior to the originally destruction of the space pirate base on Zebes, this flagship was created to help secure the planet, but an attack by the Galactic Federation crippled it, preventing it from performing its primary purpose of orbiting the planet, and this led to Samus' easy access to landing on its surface.
Nearly being scrapped, it was instead brought back into service during the phazon crisis, and was heavily modified with new pirate weaponry. It went on to hold off a fleet of ships that had come to aid the fleet already stationed at Norion during its invasion by the space pirate forces as well as Dark Samus herself. With its phazon enhanced weaponry, it easily held the less powerful ships at bay long enough for the retreat to be initiated.
After this it fought against the Galactic Federation fleet over the pirate homeworld, along with several other ships, but were ultimately defeated due to to being overwhelmed as the rest of the fleet had been sent to Phaaze. Surviving being destroyed, it came under the control of pirate commander Chitor after its phazon-based weaponry and defenses failed due to a lack of new phazon to fuel them. The ship was then used to carry supplies to Zebes in order to aid in the rebuilding of the hidden pirate base their.
It was eventually brought to the Ovias sector in order to aid in the securing of it, and after several months of disuse was used in the invasion of Lacarus Prime. During the battle its shields were damaged by Samus and her gunship, and ultimately a massive fuel gel leak occurred. The ship was then heavily damaged by Metroid Prime when it ignited the fuel gel, causing the ship to crash into the planet's surface, ultimately damaging it beyond repair.