The Solothurn S-18/100 20 mm Anti-Tank Cannon was a Swiss and German anti-tank rifle used during the Second World War. It had a semi-automatic action in a bullpup configuration. As a result of its large, powerful ammunition, the gun had a tremendous recoil, and its size made portability difficult. The feed was either from a five or (more usually) ten-round magazine that was attached horizontally to the left side of the gun. The gun used 20×105mm belted-case ammunition which it shared with the S 18-350 aircraft cannon that was developed from the rifle. A Finnish source gives armour penetration of the gun (probably achieved with the Hungarian APHE-T round, since it was the only type used in Finland) as 20mm at a 60-degree angle at 100-metre distance, decreasing to 16mm at 500 metres.