Military trench diggers (7)
I believe the answer is:
sappers
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">military trench diggers</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 sappers that I've seen before include "Military engineers" , "Royal Engineers" .)