The Solothurn S 18-1000 was a Swiss-built 20 mm Anti-Tank rifle which was an upgraded version of the earlier S 18-100. It saw service in both the Axis and Allied forces and was deployed in many theatres of operations through the war. Despite its weight and size, it was appreciated by the troops that used it.
An S 18-154. Source: Sa Kuva
Design and Development
When the Treaty of Versaille was signed on 28th June 1919, the once magnificent German arms industry found itself under considerable restrictions. One of these restrictions was on the development of large caliber weapons capable of taking out tanks, similar to the TankGewehr M1918 developed by Mauser during the First World War.
To bypass these restrictions, Rheinmetall set up a subsidiary in Switzerland in 1929, Waffenfabrik Solothurn. This meant that German engineers could design, test and build weapons without the worry of the victorious Allied powers faulting on Germany for not holding to the Versailles Treaty. In 1930, they had developed the 20×138mmB cartridge or ‘Short Solothurn’, which was one of the most powerful 20 mm rounds in existence at the time and remained in use until the early 1950s. Soon after the development of the 20 mm cartridge, the Solothurn ST-5 anti-aircraft gun was produced and, from here, Solothurn started a journey that saw the development of many weapons, all using the 20 mm Solothurn round. The first foray into anti-tank weapons was the 2 cm Tankbuchse S 5-100 in 1932, which was an offshoot of the ST-5 and was impractical for its intended use, which meant it was not fully developed. In 1933, development started on a more practical anti-tank weapon, the S 18-100. This 44 kg, bull-pup, hard-hitting gun was placed on the export market in 1934 and was soon picked up by Italy, Hungary, and the Netherlands to name but a few.
It was decided in the late 1930s that the S 18-100 series needed a more substantial upgrade (previously the S18-100 saw minor improvements in the S 18-150, S 18-154 and S 18-500). Using the improved 20×138mmB cartridge, also known as the ‘Long Solothurn’, and adding a longer barrel, a ‘harmonica’ style muzzle break, improved action and some other minor modifications, a newer, more hard-hitting version of the Solothurn was created. The weapon worked on a short recoil system, meaning that the barrel moved slightly backward when fired. Because of the large recoil spring, it required a ratchet crank in order to pull the bolt back to set it up for operations. Once the bolt was pulled back, a magazine could then be loaded. When fired, the barrel recoiled, moving the attached rotary bolt and unlocking the bolt which then ejected the spent casing. The bolt is then driven forward by the large spring, loading a fresh cartridge from the magazine. Like many anti-tank rifles of the time, it came with an integrated bipod, which allowed for some recoil absorption, and a single adjustable monopod to the rear just ahead of the cushioned butt plate. These modifications increased the weight from a substantial 45 kg to a hefty 53 kg and saw Solothurn develop the SO9 carriage for it. This was a simple two-wheeled carriage which had space for two ammunition boxes and allowed for free traverse. It also had the ability to change the elevation through a screw. The split trails could be flipped forward and locked together to allow the gun team to move the gun with ease to a new position.
A brochure picture of a Swiss soldier firing an S 18-1000 on the SO 9 carriage. Source:- Axishistory
During Solothurn’s trials in 1939, it performed quite respectfully. The much improved ‘Long Solothurn’ round coupled with the 144.78mm (57 inch) long barrel gave it a muzzle velocity of 910 m/s and could penetrate 35 mm of armor plate at 300 meters.
On the Market
After trials, Solothurn approved the S 18-1000 for production. The design of the weapon, alongside its impressive performance, saw it gain a lot of attraction on the international market.
A fully kitted out S 18-1000. Source:- MurphyAuctions
The first nation to acquire the S 18-1000 for service was the Swiss Army, which placed an initial order for 60. These were designated Tankbüchse Solo 40 and were delivered in the first quarter of 1940. Another 33 were ordered as the Swiss Army was impressed by its capabilities, bringing the total in Swiss use to 93. One rifle was installed to the prototype Type 41 Patrol Boat Uri.
The Netherlands had bought six S 18-15 in 1937 for trials but rejected them upon seeing the initial results for the S18-1000. A definitive order for 662 S18-1000s was placed in late 1938, divided as 340 for the Royal Netherlands Army (Koninklijke Landmacht) and 322 for the Royal Netherlands East Indies Army (Koninklijk Nederlands Indisch Leger; KNIL). By the time of the German invasion in May 1940, 125 Dutch Army and 72 KNIL rifles had been delivered.
The Italians also looked at the S 18-1000 after rejecting the S 18-100 in 1934. They placed initial orders in 1939 for trials and the first pieces arrived in early 1940 being designated Carabina “S”. At the conclusion of the trials, the Italian Royal Army (Regio Esercito) wanted to equip every infantry battalion with 6 pieces. It is unknown how many were delivered to the Italians, but it is thought to be around 578 of the estimated 1,131 required. The main reason for the lack of deliveries was that Switzerland was placing restrictions on the exportation of war materials to any belligerent nation in 1940.
With Europe being engulfed by war, Sweden started to look towards protecting itself. In 1940, it made inquiries to purchase 480 S 18-1000s. These were approved as Sweden was a neutral country and thus not subjected to Switzerland’s restrictions. Using balance of trade payments with Germany for steel, the rifles arrived between 1940-1941 and were designated 20 mm pansarvärnskanon m/1939.
Hungary had purchased the S 18-100 in 1935 and were producing their own licensed variant, the 36M 20mm Nehézpuska. After the Slovak–Hungarian War, they realized that the 36M was in need of upgrading and purchased around 50 (sources vary) of the new S 18-1000 in early 1940, but as restrictions became tighter, they were unable to purchase more and so production continued on the 36M until 1943.
The US Army had concluded in the mid-1930s that the .50 M2 Heavy Barrel (HB) machine gun would be adopted as the official light anti-tank gun and general vehicle-mounted machine gun. However, observations made during the Spanish Civil War suggested that the .50 might not be sufficient in future conflicts as an anti-tank weapon, so work was put towards creating an anti-tank gun, the 37 mm Gun M3. While the infantry branch championed such a move, the cavalry branch and US Marine Corps still expressed interest in a light anti-mechanization weapon. To this end, the Ordnance Department ordered two S 18-100 rifles in 1939, along with 2,000 rounds of ammunition for trails by the Infantry and Cavalry Boards at the Aberdeen Proving Grounds. The results of the trials were unsatisfactory, but as the trials were coming to a close, the S 18-1000 was ready, and so, an example was obtained for testing. Arriving in April 1940, it performed better than its predecessor and was passed on for further trials by both the Infantry and Cavalry boards. The S 18-1000 was seen as superior in performance to the M2 machine gun, so an order was placed with Solothurn for a further 50 models with 50,000 rounds of ammunition which would be standardized as the 20 mm Automatic Gun T3. During negotiations with Solothurn though, things turned difficult. This was down to Solothurn’s parent company – Rheinmetall – specifically forbidding the sale of Solothurn’s anti-tank rifles to any country without its approval, and so, the acquisition was abandoned.
A picture showing the US Army trial of the Solothurn at Aberdeen Proving Ground on 9 April 1940. Source: Reddit
Finland was attempting to modernize its military inventory in the run-up to the Winter War of November 1939. As part of this, one S 18-1000 was purchased by the Puolustusministeriö (Ministry of Defence) in August 1939 (one of the first models as it had the serial number of 4 stamped upon it) for testing. Unfortunately, though, any chance of purchasing more was rendered difficult due to the Soviet-German Molotov-Ribbentrop Pact which saw Germany restrict arms shipments to Finland through its territory.
Swedish presentation of the Solothurn S18-1000 (or 20 mm pkvan m/39) with characteristics
Solothurn at War
When the German military crossed the Polish border on the morning of 1st September 1939, the nations of Europe realized that another great war was unavoidable. The armies mobilized against the threats and so the Solothurn S 18-1000 was to be put to the test.
After Poland fell to the joint German-Soviet invasion, the world expected a bloodbath in the West between the Anglo-French alliance and Germany, but outside a few skirmishes on the border nothing occurred for eight months in what became known as the ‘Phoney War’.
It is not known if the single S 18-1000 that Finland acquired before the outbreak of the Winter War was ever issued to combat troops and so it is thought that the S 18-1000s baptism of fire occurred during the German invasion of the Netherlands. The Germans launched their offensive against the Western allies on the morning of 10th May 1940. The 4th Panzer Division was given orders to secure the strategically important Dutch city of Maastricht. The city contained vital bridges over the Maas River, as well as sat to the north of the Belgian Fort Eben-Emael. The Dutch had been on alert since 7th May and troops had been deployed to areas the General Staff felt were vital to the German line of attack. Sergeant Van der Sande was in command of an anti-tank rifle section containing two S 18-1000s and was ordered to deploy his weapons near the two bridges of Wilhelminabrug and Sint Servaasbrug and delay any German advance. At 05:15 on the morning of the 10th May, the first German vehicles were spotted by der Sande’s section and the two anti-tank gunners, Rietveld and Plusjé, prepared their weapons. The order to fire was given and within minutes 2 armored cars were out of action and a third was severely crippled. The Germans reacted by bringing up a 37 mm anti-tank gun and firing at the defensive position forcing the surviving Dutchmen to retreat across the river. The action helped delay the German vanguard enough that the two bridges were blown at 06:00.
Sergeant Sande and his men were not the only group of Dutchmen with Solothurns that were doing their part to delay the advance. A kilometer north of the Wilhelminabrug Bridge was the railway bridge and another strategic objective for the Germans. A platoon of 35 Dutch soldiers, with a pair of Solothurns, held their position against a mainly infantry assault. Soon the lieutenant ordered a withdrawal across the bridge and within moments the bridge was blown. However, the action did not stop there. The German infantry force soon received reinforcements and attempted to secure the bridge in order to effect repairs. Two armored cars attempted to cross the river but were destroyed by the Solothurns. A Panzer I was also disabled as it went to the edge of the riverbank to provide suppressive fire. The fighting became intense and more armor was brought forward, including a handful of Panzerjäger I tank destroyers (two were subsequently knocked out by the anti-tank rifles) and soon the Dutch found themselves overwhelmed. The Battle of Maastricht ended in the early afternoon with a ceasefire, but despite the Dutch loosing, their bravery and the hard-hitting power of the Solothurns accounted for several German AFVs.
The German Army is known to have acquired a number of Solothurn S-18 rifles, including the 1000 model, and deployed them alongside their own anti-tank rifles. What is not know is exactly how many or their exact deployment. The table of organization and equipment for a German Infantry division in 1940 put the complement of ATRs at 108 per Infantry Division with each of the 36 Rifle Companies containing an anti-tank rifle section of 3 rifles, the most numerous being the Panzerbüchse 39. Against the main French tanks, Hotchkiss H35 and Renault R35, any anti-tank rifle would be effectively useless except at extremely close ranges.
An S 18-1000 mounted on an Sd.Kfz. 250. Source: Reddit
A propaganda picture of Italian Bersaglieri manning a “36M Fucile Contracarro da 20-mm Solothurn” in the North African desert. Source: Axishistory
The next known usages of the Solothurn S 18-1000 was by the Italians in the Desert Campaign. Italy received its first batch of 100 Solothurn S 18-1000s in late 1940 and immediately shipped them to their troops serving in the African desert. It was intended to arm every Italian division with an anti-tank company that contained 3 platoons of 4 Solothurns each, but this was not possible, so the S 18-1000s were given to elite units like the Bersaglieri (an Italian light infantry unit) and Compagnie Auto-Avio-Sahariane (Auto-Saharan Companies, long range desert units). More Solothurns started to arrive at the end of 1941/early 1942 and were assigned on the basis of 9 per Bersaglieri to fit in with their intended role as light infantry. The hard-hitting power, coupled with their small silhouette, meant that the weapon could be effectively used against the Commonwealth forces and their lightly armored tanks such as the Light Tank Mk.VI and Cruiser Mk.IV. The weapon also became popular with the Compagnie Auto-Avio-Sahariane, or Auto-Saharan Companies, which were the Italian version of the British Long Range Desert Group (LRDG). When the Camionetta Desertica SPA-Viberti AS.42 arrived in September 1942, several were equipped with the S 18-1000 to help in the company’s mission of hunting down the LRDG. In this role, the S 18-1000 succeeded, as the LRDG operated in similarly open-topped and lightly armored four-wheel vehicles.
An AS.42 somewhere in the Libyan desert, 1942. Source:- tapatalk.com
Another Italian use of the S 18-1000 that is often forgotten is the L3 cc (controcarro or anti-tank). Using the Carro Veloce L3/35 light tank as a base, the twin 8mm Bredas were replaced with the Solothurn. An exact number of how many were produced is not known, but it was not many and they arrived in Libya in late 1942. They performed adequately in the Axis retreat through Africa and some participated in the famous Battle of Kasserine Pass.
An abandoned L3 cc. Source:- tapatalk.com
As the weapon was deployed to Italian frontline units in Africa, it was inevitable that some would fall into the hands of the Commonwealth forces they were fighting against. The Australian 2/2nd Anti-Tank Regiment had one of its reserve batteries equipped with a number of captured Solothurns during the Syria–Lebanon Campaign. How widespread it was among other Commonwealth units is not known, but it can be speculated that several Solothurns would have been repurposed.
It is also alleged that some S 18-1000s of the Royal Netherlands East Indies Army fell into the hands of the Imperial Japanese Army who found them more reliable and effective than their own Type 97 anti-tank rifle and used them until they ran out of ammunition.
End of Life
With the rifle weighing 53.5 kg/118 lb empty (54.7 kg/120.6 lb with 10 round magazine attached), as well as the increasing amount of armor being put onto AFV, it meant that the Solothurn was losing its place on the battlefield. As the war raged on the Solothurn was seen less and less and it is believed that the last combat uses of the S 18-1000 were by Italian forces of the National Republican Army as they fought frantically against the Allied advance. A select fire version was produced in 1942, designated the S 18-1100 ‘Universalwaffe’ (universal weapon) and was sold with a specialized AA mount (SO 11) to be able to engage aircraft, as well as the SO 9 carriage for use against AFVs. Not many, a few hundred, of these were produced until production was stopped at the end of 1942/early 1943.
The S 18-1100 on the SO 11 carriage from a Solothurn brochure. Source:- Axishistory
After the war, hundreds of S 18-1000s were put into the lucrative US gun market where they were sold off to gun collectors and enthusiasts. Today it is a rare find but there is still a number of them in the hands of collectors and occasionally they may be found upon the firing ranges.
A post-war advert with an embellished background of the S18-1000. Source:- 2cm flak
Anti-Tank Rifles are often confused with Anti-Tank Guns, both in nomenclature and usage. ATRs are designed to allow the standard infantry unit to disable armored fighting vehicles and work in conjunction with other weapons, like dedicated anti-tank guns. When ATRs were developed during the interwar period, they were effective if albeit bulky but they offered a cheap and more mobile alternative than anti-tank artillery.
The Solothurn S 18-1000 could be called the pinnacle of anti-tank rifles. The ‘Long Solothurn’ round allowed it to keep up with armored development until 1942 but it quickly dropped off when the Allies started to deploy vehicles like the M3 Grant/Lee and M4 Sherman medium tanks in large numbers. The two biggest drawbacks to the S 18-1000 were its weight and its complicated system which meant that misuse or lack of attention could damage the weapon easily. With the heavy deployment of shaped charges and rocket-propelled grenades in 1943, the infantry now had a more effective and lightweight anti-tank weapon that was more viable than the ATRs of the previous few years. The Solothurn, along with its brothers, were forced in obsolescence and became curiosities.
Zaloga, Steven. The Anti-Tank Rifle, Osprey Publishing, 2018
Weeks, John. Men Against Tanks: History of Anti-tank Warfare, David & Charles, 1975
Illustration of the Solothurn S 18-1000 made by Yuvnashva Sharma. Funded by our Patreon campaign.