The U.S. submarine chasers in WWI were powered by air-started, 6-cylinder 220-hp Standard Motor Construction Company gasoline engines. These were enormous, open-crankcase engines weighing 6,300 lbs. each (x3: starboard, port, and center engines).
For a sense of just how big: 10" bore, 11" stroke. Imagine being in a small engine room on a wooden boat with three of those running. To guard against explosions due to the room filling up with gasoline fumes there were ventilation fans that had to be run continuously, any time the engines were running. Even so, there were many cases of explosions and fires on chasers. For example, see this page on SC 343.
In this photo, probably on SC 248, we see engine maintenance in progress. Thanks to Don Peteya for submitting the photograph (one of a larger set) to The Subchaser Archives.
--Todd Woofenden, editor