https://en.wikipedia.org/wiki/Prison_ship
https://www.liquisearch.com/list_of_us_military_prisons/current_military_prisons/united_states_navy
https://www.pri.org/stories/2017-11-24/us-coast-guard-operating-floating-prisons-pacific-ocean-outside-us-legal
This is part I liked about the wiki link.
>A prison ship, often more precisely described as a prison hulk, is a current or former seagoing vessel that has been modified to become a place of substantive detention for convicts, prisoners of war or civilian internees.
https://en.wikipedia.org/wiki/Civilian_internee
>A civilian internee is a civilian detained by a party to a war for security reasons.