Equipment developing no rust, etc, came (13)
I believe the answer is:
Here is my best explanation:
'equipment' is the definition.
(I've seen this before)
'developing no rust etc came' is the wordplay.
'developing' indicates anagramming the letters.
'norustetccame' anagrammed gives 'ACCOUTREMENTS'.
(Other definitions for accoutrements that I've seen before include "Trappings", "clothing", "Equipment", "Appurtenances", "Paraphernalia", "Gear", "Kit" and "Soldiers outfit other than weapons and garments".)