US army survey estimate 1000 missing (5)
I believe the answer is:
recon
'survey estimate 1000 missing' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'us army' is the wordplay.
I cannot really understand how this works, but
'army' could be 're' (Royal Engineers army regiment) and 're' is present in the answer.
The remaining letters 'con' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for recon that I've seen is " Abbreviated word for a military observation".)