Working in my shop, I heard the sound of multiple round engines. Ran outside and there were four AT-6s practicing diamond formation. I watched nearly 1/2 hour as they disappeared over trees and I could tell by the props as they turned to circle back. An airshow like performance of turning and circling. Standing, watching, I enjoyed an old man type imagination to realize these same sounds were heard 80-85 years ago in Texas training fields. The sounds of the props and engines only T-6s make. One AT-6 turned back, flew over trying to get his smoke to work. It looked more like puffs from a steam train. He then turned and rejoined the other three who had also turned back. They then continued on towards home, calling it a day.