Lillie Lightship is a special and much-loved lightship, placed at Dender Rocks to warn shipping of potential hazard. The Star Fleet have the contract to provide her with the necessary fuel to keep her light shining.
She appeared for the first time in a small cameo role in 'Sunshine', although she had more important roles in later episodes, particularly Regatta, in which she was hit by a blinded tramp steamer that made a hole in her side. She was saved by Grampus, and repairs at Lucky's Yard allowed her to view the annual regatta. Lillie's light failed for a second time in Bigg Freeze, which meant that the Star Fleet needed to find another source to guide Hercules into the estuary with the liner Vienna. Hercules appears to have 'a special place in his heart' for Lillie.