The sound truck was actually used in Brinkley’s 1932 campaign (not in 1930), and it is documented that Huey Long was using sound trucks, to great advantage, as early as 1930. So no: Brinkley didn’t invent the sound truck. But he may have invented the idea that the sound truck would play pre-recorded speeches and not just warm-up music. We spent a long, long time on this note before deciding to move on. The point is, he either invented it, or he was a very early adopter/pioneer.