RA's equipment fails (5)
I believe the answer is:
tanks
I believe this is a double definition.
'ra's equipment' is the first definition.
(vehicles used by the Royal Artillery)
'fails' is the second definition.
(tank can mean to fail or do badly)
(Other definitions for tanks that I've seen before include "Armoured military vehicles" , "Bombs" , "Armored military vehicles" , "Reservoirs - military vehicles" , "Armed vehicles" .)