Combat vehicle (4)
I believe the answer is:
tank
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">combat vehicle</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tank that I've seen before include "See 1 Across" , "Fighting vehicle" , "Large container for liquid" , "Armoured vehicle - container for liquid or gas" , "Combat vehicle" .)