Thanks John & Paul, I think we have figured it out. I have photos of the Royal Family with huge Daimler Knights and the Knight engine was invented by an American, but he couldn't get anyone in NA interested [till much later] so he licensed Daimler , Minerva, and a few other European Companies to build engines. They were in production till the early 30s, by which time the poppet valve engines were just about as quiet and didn't lay down a smokescreen. A mid 20s invention [the Skinner oil rectifier] helped the smoke problem, but it was too late.
Hal