Curse when senior officer's overcome by sudden rush (7)
I believe the answer is:
scourge
'curse' is the definition.
('scourge' can be a synonym of 'curse')
'senior officer's overcome by sudden rush' is the wordplay.
'senior officer' becomes 'co' (commanding officer).
'overcome by' indicates putting letters inside.
'sudden rush' becomes 'surge' (I've seen this before).
'co' going inside 'surge' is 'SCOURGE'.
'when' is the link.
(Other definitions for scourge that I've seen before include "Whip, flog" , "Cause great suffering to (someone); whip" , "One providing lashings" , "Punish severely" , "administer punishment" .)