... SERVICE UNITS No. 31 AN R.A.F. SIGNALS GROUP: By MEL Even though information likely to be of use to the enemy has to be kept so close a secret, it is fairly safe to assure the lay public that signalling in the R.A.F. is rarely done by the flag-wagging method, and even whistling and shouting out such expressions as Oi and Hi can be ruled out. Even with these manifest handicaps the message ...