The University horn on the Cessna looks very much like the horn on the chopper in Apocalypse Now. I thought for sure that I had posted a still of it, but can't find it. Oh well. Makes sense that they would use it for the film. It's period correct and small enough to fly. I have no idea what else was used in the war. But it does seem that both were used extensively, from the lit. Was there actually any disagreement about that?