I don't know anything about Erin writing a song specifically about the RAF (Royal Air Force), but my best guess would be the song "Aspera" off of We Will Become Like Birds. The motto of the RAF is "per ardua ad astra" which (roughly translated) means "to adversity to the stars" or "through struggle to the stars". Hope this helps.
Primarch02:
I don't know anything about Erin writing a song specifically about the RAF (Royal Air Force), but my best guess would be the song "Aspera" off of We Will Become Like Birds. The motto of the RAF is "per ardua ad astra" which (roughly translated) means "to adversity to the stars" or "through struggle to the stars". Hope this helps.