One of the finest (and most expensive) submachineguns made prior to World War II, the Steyr-Solothurn S1-100 has only a short career.
The story of the S1-100 starts in around 1919, when German arms-making company Rheinmetall produced a prototype submachine gun designated MP.19. This weapon was developed by Lous Stange to the same specifications as Schmeisser's Schmeisser MP.18/I, but MP.19 came too late to see any action during WWI. After the end of WWI, Germany was severely limited in the design and production of small arms by the Treaty of Versailles.
When Hitler came into power, German military-oriented companies began to move the research and development outside of Germany to avoid treaty limitations. In 1929, Rheinmetall purchased the small Swiss-based company Wafenfabrik Solothurn, which was used to finalize some Rheinmetall small arms which were developed under secrecy in Germany. One of those weapons was an improved version of MP.19 submachine gun, which was announced by Waffenfabrik Solothurn under company index "S1-100". This was an excellent weapon, reliable, controllable and accurate, but Solothurn company lacked production capabilities. To make guns on an industrial scale, Solothurn teamed up with the famous Austrian gun-making company Waffenfabrik Steyr, and formed the trade company Steyr-Solothurn Waffen AG in Zurich, Switzerland. This company sold weapons designed by Rheinmetall and Solothurn and made by Steyr, and the S1-100 submachine gun was among the first products of this international conglomerate.
In 1930, the Austrian police adopted the S1-100 as the Steyr MP.30, chambered for then-standard Austrian 9x23 Steyr pistol cartridge. It was also exported to Chile, Bolivia, Uruguay and El Salvador, and was sold in limited numbers to China, in 7,63x25 Mauser caliber. Portugal adopted the S1-100 in 7,65x22 Luger caliber in 1938, and in 1942 purchased more S1-100's from Steyr, but this time in 9x19 Luger. For the South American markets, Steyr produced a version of the S1-100 in .45ACP caliber; this version was distinguished by an additional pistol grip under the forearm. The Austrian army adopted the S1-100 as Steyr MP.34, chambered for the powerful 9x25 Mauser ammunition.
When Hitler's Germany occupied Austria in 1938, it quickly consumed most of Austrian MP.30's and MP.34's, and after rebarreling them to 9x19 ammunition these weapons were issued to German troops as the MP.34(ö). Production of Steyr-Solothurn submachine guns ceased in around 1940, when, under German administration, it was replaced in production at Steyr by the much simpler and less expensive MP-40 submachine gun of German design.
The Steyr-Solothurn S1-100 submachine gun was a blowback operated, selective-fire weapon which fired from the open bolt. Unlike most other submachineguns, the return spring was located in the buttstock and was linked to the bolt via a long push-rod, pivotally attached to the rear of the bolt. The basic action of the gun was accessible through the top cover, which was hinged at the front and opened up and forward to expose the bolt and trigger unit below it. The fire mode selector was made in the form of a sliding switch, located at the left side of the stock. Early guns had a Schmeisser-style bolt-locking safety in the form of hook-shaped cut which was used to engage the bolt handle when bolt was cocked. Later on, additional manual safety was added to the top cover, in front of the rear sight. This safety locked the bolt either in cocked or closed position. The feed was from left side, with magazine housing slightly canted forward for more positive feeding; ejection was to the right. The magazine housing had an unusual magazine filler device, with slots for the magazine at the bottom and for the stripper clip - at the top. The removed magazine was inserted into this device from the bottom, and then the shooter placed the stripper clips into the top of device and pushed cartridges down into magazine. Four standard 8-round clips were required to fill the magazine.
All S1-100 guns were fitted with a wooden stock with a semi-pistol grip. The barrel was enclosed into a perforated jacket, which had provisions for mounting a bayonet. Sights included hooded front and tangent type rear, marked from 100 to 500 meters. One of the most unusual accessories, which was briefly advertised for S1-100 during mid-1930s, was a compact machine-gun type tripod, which was to provide additional stability for the weapon when firing from the ground. It seems that this tripod was never made in quantity.