Type of combat here, warn craft at sea (6,7)
I believe the answer is:
trench warfare
'type of combat' is the definition.
(I know that trench warfare is a type of armed combat)
'here warn craft at sea' is the wordplay.
'at sea' is an anagram indicator.
'here'+'warn'+'craft'='herewarncraft'
'herewarncraft' is an anagram of 'TRENCH WARFARE'.
(Other definitions for trench warfare that I've seen before include "Combat from dug-in positions" , "Combat on Western Front in WW1" , "combat in the field" .)