Small rescue vessel, in 1945, liberated part of the British Isles (4)
I believe the answer is:
sark
'1945 liberated part of the british isles' is the definition.
I can't tell whether this defines the answer.
'small rescue vessel' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'rescue vessel' becomes 'ark' (I've seen this before).
's'+'ark'='SARK'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for sark that I've seen before include "Scottish shirt; island" , "Small Channel Island" , "Hereditarily-ruled Channel Island" , "Island in English Channel" , "One of Channel Isles" .)