Before I learned that “CD” meant a certificate of deposit or a compact disc, it meant civil defense to me — the homeland security type of civil defense.

The term was common during the early years of the so-called Cold War after World War II, when Americans were braced for a possible nuclear exchange with the Soviets.

The saber-rattling coming out of North Korea in recent months reminds me of those years from my youth.

It didn’t help that on Monday and Tuesday, television programs on four channels — count ‘em, four channels — were interrupted by those irritating tones and the words, “This is a test …” It even happened on a radio station I was listening to. All coincidence, I assume.

Mostly, the emergency system is activated for local weather warnings. While those interruptions are important, they don’t necessarily suggest it’s the end of the world as we know it. Pun intended.

My father was an amateur radio operator. You may have heard it called ham radio. The hobby became crucially important whenever natural disasters destroyed traditional means of communication. Technological advancements like cell phones may have reduced the emergency role of “hams,” but when large areas are literally wiped out — like we’ve seen happen in Puerto Rico this year — ham radio operators even today are sometimes the best, if not the only, link survivors have to the rest of the world.

Dad’s involvement with amateur radio led him to volunteer for local civil defense planning in the county where we lived in North Carolina. School students were given lessons on what to do if a nuclear bomb landed nearby. Does anyone remember “duck and cover” drills? Public buildings were identified as shelters where people could wait for fallout to disperse. Evacuation routes were marked. Some families even designated a corner of their homes’ basements as bomb shelters, and stocked them with supplies.

Those were tense times, and I’m glad I wasn’t old enough then to fully understand them. Some worry we are now facing a repeat. Let’s hope world leaders are composed.

The broadcast alerts that predated the tests we hear today on radio and television involved a network known as CONELRAD, an acronym for Control of Electromagnetic Radiation. It was intended to allow continuous broadcast of civil defense information to the public through designated AM radio stations in the event of enemy attack. Those stations had the capability to switch transmission to broadcasts enemy bombers couldn’t use to home in on population centers. In World War II, German radio stations were used as broadcast beacons by Allied bomber pilots.

During tests, designated stations would practice switching transmitters. In the event of the real thing, AM radio stations would broadcast only on either the 640 or 1240 frequency, while television and FM stations would go silent. AM radios of that era even had dials with both CONELRAD frequencies marked with triangles.

In 1963, after intercontinental missiles made bomber attacks less likely, CONELRAD was replaced by the Emergency Broadcast System, followed by the Emergency Alert System in 1997. While CONRELAD was intended only for use during enemy attacks, subsequent systems are available for other warnings, like bad weather.

Today, the tests seem to happen at the worst possible time, like when the villain is revealed at the end of a two-hour murder mystery. But I won’t quarrel. I’m glad that usually, “this is only a test.”

Gene Deason is editor emeritus of the Brownwood Bulletin. His column appears on Fridays. He may be contacted at news@brownwoodbulletin.com.