In the United States, traditionally civil defence was largely during WW1 and WW2, as well as the Cold War vis-à-vis atomic attacks. However, in peacetime there have been ample opportunities to set up a coördinating body for civil defence efforts, such as the 1904 San Francisco earthquake. For the sake of the OP and the WI, I'm using the Great New England Hurricane of 1938 as the POD here, not only because it is an important event in local history, but also since many people were unprepared for dealing with hurricanes (not helped by the Weather Bureau's bad forecasting).
So, how would the Office of Civil Defense operate if the 1938 hurricane was the impetus?
So, how would the Office of Civil Defense operate if the 1938 hurricane was the impetus?