The Solothurn S-18/100 20 mm anti-tank cannon was a German and Swiss 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. A variant of this design, the Solothurn-Arsenal, was manufactured without license in Estonia before WW2; however only 20 were produced prior to Soviet occupation.^[1]

Solothurn S-18/100 20 mm anti-tank cannon
Hungarian soldier with the Solothurn S-18/100
Type	Large caliber rifle, anti-materiel rifle
Place of origin	Nazi Germany Switzerland
Service history
Used by	See Users
Wars	Slovak-Hungarian War World War II
Production history
Produced	1934-1943
Variants	Solothurn S-18/1000, Solothurn S-18/1100, Solothurn-Arsenal
Specifications
Mass	45 kg without magazine
Length	1,760 mm
Barrel length	925 mm
Cartridge	20×105mmB
Caliber	20 mm
Action	API Blowback
Rate of fire	Semi-automatic
Muzzle velocity	735 m/s with a Hungarian APHE-T round
Effective firing range	400 m (for penetration of 50mm armor)
Feed system	10-round detachable box magazine
Sights	A dedicated scope

In March 1940, with funds collected in Switzerland to help the Finnish war effort in the Winter War, Finland bought twelve S 18-154 anti-tank rifles from Solothurn, though the purchaser was nominally the Swiss army. The weapons arrived into Finland during the spring after the war had ended, but they were later used in the Continuation War. However, the guns were soon found to be obsolete in their intended role. Various models of the S-18 series, including the Solothurn S-18/1000 and the Solothurn S-18/1100 were also used by Switzerland, the Kingdom of Hungary, Nazi Germany, the Kingdom of Italy, and the Netherlands.

The Waffenfabrik Solothurn [de] firearms company was owned by the German firm Rheinmetall, and used the Swiss company to manufacture arms which were prohibited for manufacture by any German firm to get around arms limitations imposed upon them at the end of the First World War.