Sacrifice and explosive combat at sea (8)
I believe the answer is:
hecatomb
'sacrifice' is the definition.
(hecatomb is a kind of sacrifice)
'explosive combat at sea' is the wordplay.
'explosive' becomes 'he' (abbreviation for high explosive).
'at sea' is an anagram indicator.
'combat' is an anagram of 'catomb'.
'he'+'catomb'='HECATOMB'
'and' is the link.
(Other definitions for hecatomb that I've seen before include "Large-scale sacrifice" , "major sacrifice" , "Great quantity of victims" , "big sacrifice" , "great public sacrifice" .)