Soldiers to yield or retreat (6)
I believe the answer is:
recede
'retreat' is the definition.
(I know that retreat can be written as recede)
'soldiers to yield' is the wordplay.
'soldiers' becomes 'RE' (Royal Engineers).
'to yield' becomes 'cede' (synonyms).
're'+'cede'='RECEDE'
'or' is the link.
(Other definitions for recede that I've seen before include "Withdraw" , "Become more distant" , "Start balding" , "Move backward" , "Decree (anag) - ebb" .)