Drill command
(Other definitions for again that I've seen before include "Predictably perhaps" , "Here we go ___" , "Next time" , "Anew" , "Repeatedly" .)
'drill command' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for halt that I've seen before include "Falter - stop" , "Stop or pause" , "Stop, small station" , "Pull up" , "limping" .)