In Aliens (1986), the starship carrying the Colonial Marines is the Sulaco.
The Sulaco transports the marines from Earth to LV-426, where they are sent to investigate the loss of contact with the colony at Hadley's Hope. It is a military assault ship rather than a civilian transport, carrying the troops, equipment, dropship, and armored vehicle used during the mission.
The name is often confused with other ships from the Alien franchise. The Nostromo is the commercial towing vessel from Alien (1979), while Sevastopol is the space station featured in the video game Alien: Isolation. Titan is not the marines' ship in Aliens.
The Sulaco is largely seen through its operational role: the marines deploy from it aboard the UD-4L Cheyenne dropship. Its later appearance in Alien 3 also connects it to the wider series timeline.