Wartime submarine (1-4)
I believe the answer is:
u-boat
'wartime submarine' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for u-boat that I've seen before include "German World War One or World War Two submarine" , "About (anag)" , "Submersible warship armed with torpedoes" , "German WW 2 sub" , "Submersible warship of WWII" .)