Assemble artillery instead of third of army (5)
I believe the answer is:
array
'army' is the definition.
(I've seen this in another clue)
'assemble artillery instead of third' is the wordplay.
I cannot quite understand how this works, but
'artillery' could be 'ra' (Royal Artillery) and 'ra' is found within the answer.
The remaining letters 'ary' 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).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for array that I've seen before include "Rig up" , "Imposing show or military order" , "Matrix; display neatly" , "Lay out, arrange" , "Order - arrangement" .)