Plan to dump wartime rockets in river (6)
I believe the answer is:
devise
'plan' is the definition.
(synonyms)
'rockets in river' is the wordplay.
'rockets' becomes 'vis' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'river' becomes 'Dee' (River Dee).
'vis' placed inside 'dee' is 'DEVISE'.
'to dump wartime' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for devise that I've seen before include "Make (a plan)" , "Formulate or plan" , "Plan invent" , "Formulate or invent" , "Come up with, a plan perhaps" .)