A railway gun (also called railroad gun, and formerly called a railgun durring World War I and World War II) is a large artillery piece, designed to be placed on rail tracks. The first railway guns of record were constructed and used during the American Civil War. Many nations have built railroad guns, but the best known are the large Krupp-built pieces used by Germany in World War I and World War II. Some of these were so large that they required two parallel sets of tracks to support the gun's size.
Railway guns have been largely rendered obsolete by advances in technology. Their large size and limited mobility makes them vulnerable to attack, and similar payloads can be delivered by aircraft, rocket, or missile.
Note that the obsolete term railgun is usually no longer used to denote railway guns (though some sources still use it). Railgun is now usually used to describe modern electromagnetic rail cannons.