German submarines (1-5)
I believe the answer is:
u-boats
'german submarines' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for u-boats that I've seen before include "Submersible warships" , "German submarines of second World War" , "German submarines in WW2" , "Submersible ships of WW2" , "German subs" .)