The German S-mine also known as the "Bouncing Betty", is the best-known version of a class of mines known as Bounding Mines. When triggered, these mines launch into the air and then detonate at about 0.9 meters (2 ft 11 in). The explosion projects a lethal spray of steel balls and fragments in all directions. The S-mine was an Anti-Personel Mines developed by Germany in the 1930s and used extensively by German forces during the Second World War. It was designed to be used in open areas against unshielded infantry. Two versions were produced, designated by the year of their first production: the SMi-35 and SMi-44. There are only minor differences between the two models. The S-mine entered production in 1935 and served as a key part of the defensive strategy of the Third Reich. Until production ceased in 1945, Germany produced over 1.93 million S-mines. These mines inflicted heavy casualties and slowed, or even repelled, drives into German-held territory throughout the war. The design was lethal, successful and much imitated. The S-mine remains one of the definitive weapons of World War II.