Military operation ordered second row in (8)
I believe the answer is:
blockade
'military operation' is the definition.
(I know that Blockade is a type of military operation)
'ordered second row in' is the wordplay.
'ordered' becomes 'bade' (past tense of 'bid' as in to order).
'second row' becomes 'lock' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'bade' going around 'lock' is 'BLOCKADE'.
Can you help me to learn more?
(Other definitions for blockade that I've seen before include "Isolation of place by sea" , "Siege" , "Prevention of access and egress" , "Action taken to prevent entry as of goods" , "clampdown" .)