Fail to find military hardware (4)
I believe the answer is:
tank
'fail' is the definition.
(informal term meaning to fail financially)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tank that I've seen before include "Fuel store" , "Miltary vehicle" , "Large container for liquid" , "Container for liquids - military vehicle" , "Container for fish (or soldiers?)" .)