It comes as a big blow perhaps to air force? (4)
I believe the answer is:
gale
'it comes as a big blow perhaps' is the definition.
The definition suggests a singular noun which matches the answer.
'air force?' is the wordplay.
'air' becomes 'gal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'force?' becomes 'e' (E is the symbol of electromotive force).
'gal'+'e'='GALE'
'to' is the link.
Can you help me to learn more?
(Other definitions for gale that I've seen before include "Force 8 wind" , "Fierce wind" , "Bille from a bladder" , "Squall" , "A wild storm" .)