Clue: We may hear soldier bring down retardant from plane (9)
Answer: PARACHUTE
Explanation: We may hear soldier bring down retardant from plane (9)
Homophone of [*we may hear*]** PARA SHOOT** ("soldier" + "bring down") 
* A parachute would act as a retardant, i.e. it would slow you down, if you jumped from a plane.