In Gerry Andersons Thunderbirds what did " F.A.B" stand for?

it was short for..following all bulletins..when a message was received,or new orders given.it was in a 1960s annual i had as a kid,many years ago.in stingray they had a similar one which was p.w.o.r,proceeding with orders received,they were in w.a.s.p...world aquanaut security patrol.& fireball xl5,were members of w.s.c..the world space council.hope this helps.