Many World War One aircraft used rotary engines like the LeRhone rotary shown here. This type of engine was almost unique to the war. A rotary engine looks like a World War 2 radial engine, but with a crucial difference. In a radial engine, the engine stays still while the center crankshaft rotates and turns the propeller. In a rotary engine, the crankshaft stays still and the cylinders revolve around the crankshaft! The propeller was bolted to the engine block, which spun with the cylinders. Spinning the cylinders kept them cool, with no need for a radiator or cooling water, and the spinning engine acted as a flywheel. It was a very compact engine, with a great power to weight ratio. The gyroscopic effects of the spinning engine caused the airplane to have “unusual” handling characteristics, throttle control was limited at best, and the engines were prone to catching fire, so the design did have drawbacks. Nevertheless, they were very effective in early fighters, like the ones Kiffin flew. Later in the war, as engine and airframe technology progressed, inline engines became more widely used, but rotary engines were still used in some fighters through the end of the war. (Wikimedia Commons https://commons.wikimedia.org/wiki/File:Le_rhone.jpg)