Timeless weapons for military commanders (7)
I believe the answer is:
shoguns
I believe this clue is a double definition.
'timeless weapons' is the first definition.
(shotguns less t - an abbreviation for time)
'military commanders' is the second definition.
'for' is the link.
(Other definitions for shoguns that I've seen before include "Commanders-in-chief" , "Commanders" , "Rulers in feudal Japan" .)