Defensive position (7)
I believe the answer is:
redoubt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">defensive position</span>' is the definition.<br/ ><span class="explanation-format__explanation">(type of fort)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for redoubt that I've seen before include "Temporary or outward fortification" , "Tube rod used in small fortification" , "Fieldwork defending a pass" , "Military defence-work" , "Keep losing confidence in" .)