Military activity, trick by soldiers (5)
I believe the answer is:
recon
'trick by soldiers' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'military activity' is the wordplay.
I cannot really understand how this works, but
'military' could be 're' (I've seen this in other clues) and 're' is present in the answer.
'activity' could be 'con' (con is a kind of activity) and 'con' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for recon that I've seen is " Abbreviated word for a military observation".)