This order won't require attention (5,2,4)
I believe the answer is:
stand at ease
'this order' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for stand at ease that I've seen before include "take a relaxed attitude" , "Command to soldiers" , "Assume a more relaxed position (military)" , "letting attention go?" , "Instruction to soldiers - and sea state (anag)" .)