Cargo ship is an auto-flying NPC ship which travels randomly through the map. 

The ship has 1000HP and if attacked, it strikes back for 50 seconds, following the player at a higher speed than usual. After that it leaves the player alone. If attacked again, the process will repeat.

As the ship spawns, chat will show a message saying: [Server] A cargo ship has been spotted! (You can mark it using your map!)