Was their job to weaken enemy strength? (7)
I believe the answer is:
sappers
'was their job' is the definition.
I can't tell whether this definition defines the answer.
'weaken enemy strength?' is the wordplay.
I cannot really see how this works, but
'weaken' could be 'sap' (I've seen this before) and 'sap' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for sappers that I've seen before include "Military engineers" , "Royal Engineers" .)