Shipbuilders also had their own interesting wrinkle on getting enough air into the engine.

Late nineteenth century engines needed a big opening that the stokers could shovel in the coal. You couldn't pump extra air into the fire, because it would flow out too easily. The solution was to keep the entire engine room at high pressure with fans blowing air in from outside.

It gets worse. The American British Thermal Unit isn't the same as the Canadian British Thermal Unit.