Command on a submarine (4)
I believe the answer is:
dive
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">command on a submarine</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 dive that I've seen before include "Plunge into - disreputable club" , "Plunge head first" , "Leap into water" , "Plunge headfirst" , "Submarine captain's command" .)