RS 42 - Blackouts and radio silences
Blackouts and radio silences shall be carried out only in the areas, at the times, and for the periods designated by air raid warnings or orders with respect thereto issued by the United States Army, or its duly designated agency and only under conditions and in a manner not inconsistent with any warning or order. Practice blackouts shall be held only when and as authorized by the United States Army or its duly designated agency.