Water jackets were used to cool the barrels of machine guns until several years after the First World War, but modern machine guns are air-cooled to conserve weight and hence increase portability.
In a reciprocating piston internal combustion engine, the water jacket is a series of holes either cast or bored through the main engine block and connected by inlet and outlet valves to a radiator.
Equipment such as tissue culture incubators may be enclosed in a water jacket kept at a constant temperature.
[2] The concept gives its name to the water jacket furnace, a type of blast furnace, using a cold air blast, that was used for the smelting of non-ferrous metallic mineral ores.
[3] The terminology is also used for an indirect heating device used in the petroleum oil and gas industry, generally known as a water jacket heater[4] or water bath heater.