Cargo for soldiers in battle (7)
I believe the answer is:
freight
'cargo' is the definition.
(I know that cargo can be written as freight)
'soldiers in battle' is the wordplay.
'soldiers' becomes 'RE' (Royal Engineers).
'in' is an insertion indicator.
'battle' becomes 'fight' (synonyms).
're' put into 'fight' is 'FREIGHT'.
'for' is the link.
(Other definitions for freight that I've seen before include "that's carried by rail and road" , "Goods carries by large vehicle" , "Something carried" , "Goods carried by a large vehicle" , "Consignment" .)