Military personnel are members of the armed forces. Usually, personnel are divided into military branches roughly defined by certain circumstances of their deployment. Those who serve in a typical large land force are soldiers, making up an army. Those who serve in seagoing forces are seamen or sailors, and their branch is a navy. Marines serve in a marine corps. In the 20th century, the development of powered flight aircraft prompted the development of air forces, serviced by airmen. These include members of other races' military.