Rush to get missile (4)
I believe the answer is:
dart
I believe this clue is a double definition.
'rush' is the first definition.
(both can mean to move quickly)
'missile' is the second definition.
(Backwards)
'to get' is the link.
(Other definitions for dart that I've seen before include "Move quickly and suddenly" , "Small arrow" , "flash" , "Shoot out" , "Arrow - go fast" .)