Instant victory over Germany renewed strength (6,4)
I believe the answer is:
second wind
'renewed strength' is the definition.
(an additional or renewed burst of energy)
'instant victory over germany' is the wordplay.
'instant' becomes 'second' (synonyms).
'victory' becomes 'win' (I've seen this before).
'over' is a charade indicator (letters next to each other).
'germany' becomes 'd' (vehicle registration code for Deutschland).
'second'+'win'+'d'='SECOND WIND'
(Other definitions for second wind that I've seen before include "Renewed energy in effort" , "burst of renewed energy" , "Renewed energy to carry on" , "playing perhaps but not from top brass" , "Renewed vigour" .)