Ditch some gormless officers when heading north (5)
I believe the answer is:
fosse
'ditch' is the definition.
(fosse is a kind of ditch)
'some gormless officers when heading north' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'heading north' says the letters should be written in reverse.
'essof' can be found hidden inside 'gormless officers when'.
'essof' in reverse letter order is 'FOSSE'.
(Other definitions for fosse that I've seen before include "Fortified moat" , "-- Way, Roman road" , "Ditch or moat" , "Long trench or ditch" , "Long, narrow trench or excavation" .)