The first machine guns in use before World War I covered a wide range of characteristics. In addition to these heavier designs, there were also a number of lighter types. During the same period, a number of new air-cooled designs were developed that, instead of weighing well over 30 lb (15 kg), were lighter and more mobile. In World War I, they were to be as important as the heavier designs, and were used to support squads and infantry on the move, on aircraft, and on many types of vehicle, including some tanks. The two that would become critical were new medium and light machine guns. The new medium machine guns offered less, or more difficult-to-use, cooling than the heavier designs, but more than the lightest.