Perhaps U-boat, with German, to surrender (6)
I believe the answer is:
submit
'surrender' is the definition.
(thesaurus)
'perhaps u-boat with german' is the wordplay.
'perhaps u-boat' becomes 'sub' (U-boat was a type of submarine).
'with german' becomes 'mit'.
'sub'+'mit'='SUBMIT'
'to' acts as a link.
(Other definitions for submit that I've seen before include "Defer to the will of another" , "Yield; argue" , "Throw in the towel" , "Refer for judgment or consideration" , "Give way" .)