Since the 1930s. In 1939, three American Legion posts just northwest of San Francisco – in San Anselmo, Ross and Mill Valley, all just a few miles from one another – held a three-way meeting via short-wave radio. The American Legion Magazine described it as "not a stunt, but a practical demonstration of emergency communication held in conjunction with the Major Disaster Communications Committee." At about the same time, a Legion pamphlet called "In Time of Disaster" was circulating.
Today’s version is called "Disaster Preparedness and Response for American Legion Posts." Download it from the Legion’s Publications page here for September, National Disaster Preparedness Month. And find out more about the Legion’s resurgent ham radio program and Amateur Radio Club here.