Why did later machine guns use air-cooled and quick-changing barrels?

The transition to air-cooled and quick-changing barrels in modern machine guns was primarily driven by the need to make these weapons lighter, more reliable, and capable of sustained, high-speed fire.1

Early automatic weapons, such as those used during World War I and World War II, often relied on water-cooling systems to manage the intense heat generated by rapid, continuous firing. While effective, these systems were heavy and cumbersome, requiring a dedicated squad to transport and maintain the water supply.1

By shifting to air-cooled designs, engineers significantly reduced the overall weight of the weapon, increasing mobility for infantry units. To compensate for the lack of a water jacket, the development of quick-changing barrels allowed soldiers to rapidly swap out a barrel that had become overheated during sustained fire for a cool one. This innovation ensures that the machine gun can maintain its rate of fire without the mechanical failure or degradation that would otherwise occur from prolonged heat exposure.1