lightship

US /ˈlaɪt.ʃɪp/
UK /ˈlaɪt.ʃɪp/
1.

灯台船

a small ship with a flashing light on it, that stays in one place to warn ships of rocks and other dangers:

:
Barnegat Lighthouse, built in 1855, was replaced in 1930 by an offshore lightship.