A railgun is a gun that fires metal projectiles (bullets) using a magnetic field produced by electricity. Unlike conventional guns, it does not use gunpowder or other explosive propellants, and rarely needs to be cleaned or unjammed. Currently, most railguns are experimental and are not used in actual combat, but the U.S. Navy is expecting to have one operating soon. In theory, a railgun could fire a bowling-ball-sized projectile fast enough to destroy a small building, even over long distances. Railguns are usually very large and not portable because of the need for a large power supply. There have been proposals to use the same technology for non-weapon purposes, such as aircraft and spacecraft launchers and specialized tools.