Officer-to-be (5)
I believe the answer is:
cadet
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">officer-to-be</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 cadet that I've seen before include "who needs to be properly trained?" , "Officer in training" , "novice" , "not the heir" , "Apprentice officer" .)