Officer shortly making pass (3)
I believe the answer is:
col
This clue is a double definition.
'officer shortly' is the first definition.
(short for colonel; 'shortly' asks for an abbreviation)
'pass' is the second definition.
(col is a term for a mountain pass)
'making' is the link.
(Other definitions for col that I've seen before include "Pass between hills" , "Mountain defile" , "Feature of mountain" , "A pass between mountain peaks" , "Low area between peaks" .)