RESTRICTED 



Between ships using air-driven sirens rather than steam whistles, 

 the effectiveness of these signals is largely lost since there is no visual 

 portion of the signal. In this case, they can be simultaneously sup- 

 plemented by hoisting the corresponding International Code flag, or 

 the cone, ball, and drum distant signals of the old International Code. 

 A voice radio reserved for such traffic might prove more satisfactory, 

 while ships close aboard can use loud speakers to advantage. 



4 



106 RESTRICTED 



