Land forces (4)
I believe the answer is:
army
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">land forces</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 army that I've seen before include "Body of people organised for war" , "Large military force" , "A great number (of soldiers?)" , "See 21" , "Fighting force" .)