Help with very old Blazer Badge C.N.A.S
 

Hello
I wonder if anyone can help identify this blazer badge.
It has the Royal Air Force badge with Kings Crown and beneath are the initials:
C.N.A.S
My initial thoughts were Canadian Naval Air Service, which became R.C.N.A.S in 1918
I just don't know. Any ideas ??
It's my intention to move the badge on but I'd like to identify it first.
Robbo
https://i.imgur.com/cdVC1vF.jpg
https://i.imgur.com/gNDvCrK.jpg