US prison ship (4)
I believe the answer is:
brig
This clue could be a double definition.
'us prison' is the first definition.
'brig' can be an answer for 'prison' (I've seen this before). I am unsure of the 'us' bit.
'ship' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for brig that I've seen before include "Two-master; army officer (abbr.)" , "Two-masted square-rigged sailing ship" , "'Two-masted,square-rigged ship (4)'" , "Ship; a ship's jail" , "Sailing vessel or lock-up on board" .)