Friend captured in war zone where this was used? (6)
I believe the answer is:
napalm
'zone where this was used?' is the definition.
The definition suggests a singular noun which matches the answer.
'friend captured in war' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'captured in' means one lot of letters goes inside another.
'war' becomes 'nam' (informal term for the Vietnam War).
'pal' inserted within 'nam' is 'NAPALM'.
Can you help me to learn more?
(Other definitions for napalm that I've seen before include "Petroleum jelly used in bombs and flame-throwers" , "Incendiary agent" , "Incendiary bomb jelly" , "Flame thrower ingredient" , "Incendiary liquid used in firebombs" .)