The MP 18, officially known as the Maschinenpistole 18, is a submachine gun developed in Germany during World War I. It was one of the first successful submachine guns, designed to provide soldiers with a lightweight and fully automatic weapon for close-quarters combat. The MP 18 used 9mm ammunition and had a distinctive curved magazine that held 32 rounds. The MP 18 was primarily used by the German Army and became a model for future submachine guns, influencing designs like the Thompson submachine gun and the MP 40. Its introduction marked a significant shift in infantry tactics, emphasizing mobility and firepower in warfare.