Ancient war galley (7)
I believe the answer is:
trireme
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ancient war galley</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for trireme that I've seen before include "Ancient rowed ship" , "Ancient vessel with three banks of oars on each side" , "Ancient galley or warship" , "Oar-driven battleship of classical times" , "Long rowing boat" .)