Sailors tackling environment-related survey (5)
I believe the answer is:
recon
'survey' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'sailors tackling environment-related' is the wordplay.
'sailors' becomes 'RN' (abbreviation for Royal Navy).
'tackling' indicates putting letters inside (to tackle is to take possession of).
'environment-related' becomes 'eco' (I can't justify this - if you can you should give a lot more credence to this answer).
'rn' going around 'eco' is 'RECON'.
Can you help me to learn more?
(Another definition for recon that I've seen is " Abbreviated word for a military observation".)