Guard ship

1. Any vessel that makes the rounds of a fleet at anchor to see that due watch is kept at night.
2. A warship stationed at a port or harbor to act as a guard there.
3. In former times in the British Royal Navy, a ship that received men impressed for naval service, often the flagship of the admiral commanding along the coast.
4. In Soviet and Russian terminology, a guard ship (storozhevoj korabl') is a small, general-purpose patrol or escort vessel.