The time between the World Wars was that of rapid technical progress. Even tanks, a relatively new invention, could become obsolete quickly. Even though only several wealthy countries could afford a large number of the newest tanks for their armies, experimental vehicles and small batches cropped up in many nations. Sweden, who managed to retain neutrality during WWI, was among them. Its army was engaged in a lengthy and difficult search for a suitable tank. The search ended with the acceptance of the Strv m/31, or L-10, which begat a whole family of armoured vehicles.
Do it yourself
The first success for Sweden during the interbellum years was the establishment of contacts with German defense companies. Under the Treaty of Versailles, Germany was not allowed to develop or produce new types of armaments. Tanks were strictly forbidden. It was allowed to produce a limited amount of armoured cars for police forces. Nevertheless, Sweden managed to purchase parts for 10 light LK-II tanks from Germany, which were assembled at a shipyard in Stockholm. The tanks were first indexed Pansarvagn fm/22, but then received the name we know them by today: Stridsvagn m/21.
Overall, the military was satisfied with their purchase. Even five years after the end of WWI, the LK-II was not yet obsolete. It had decent off-road performance, especially for a tank of its class, and the crew conditions weren't bad for the era. The only serious drawback was the lack of a cannon. It also turned out that 10 German tanks was all that Sweden could hope for. There was no possibility of ordering more LK-IIs, and none was expected to come up.
Meanwhile, Sweden was not living under a rock. Information about new types of armoured vehicles reached the country, especially British and French models. They knew about the Medium Tank Mk.D, the Medium Tank M1921 that was built on its chassis, and Medium Tanks Mk.I and Mk.II. Information on these vehicles was available from multiple sources, including "Die Kampfwagen fremder Heere", which was published in 1926 in Berlin. Hauptmann Fritz Heigl from Vienna was directly connected with the publication. He turns up in this story later.
Renault FT during trials of radio equipment, 1924. The gun was removed from the turret.
Incoming information suggested that tanks were developing, and their maneuverability grew as much as their firepower. Unfortunately, even buying a British Medium Tank Mk.I was impossible at the time. The French Renault FT was the bestseller on the world market. Even Sweden's eastern neighbour Finland had 32 of these tanks.
In the fall of 1923, the Swedish KAF (Kungliga Arméförvaltningen, the Royal Army's Supply Directorate) approved the purchase of one Renault FT. A tank armed with a cannon in a Berliet turret was obtained. The Swedish military was quickly disappointed by its purchase. The Swedish infantry guards regiment (Svea livgarde) which received all of Sweden's tanks nicknamed the Renault FT "Putte", or "angel". After the LK-II, which comfortably fit four tankers, the two-man Renault FT felt like a coffin. It was also slower than the German tank.
The only advantage of the French tank was the cannon, which was removed and installed into a Strv m/21 in 1924. The weapon did not return to the Renault FT. In August of 1926, when the tank's engine gave out, it was written off without any regrets and used as a shooting range target.
Trials of the Renault NC-27, which also led to nothing. The failure of this tank was the last straw, and Sweden decided to design its own tank.
The second attempt of "French intervention" was made in November of 1927, which Sweden began talks to purchase a Renault NC: a modernized Renault FT with thicker armour, a 62 hp engine, and a new suspension. KAF decided to buy a single tank. Trials held at the Järvafältet proving grounds to the north-west of Stockholm brought disappointment once more. The tank broke constantly. Gearbox issues were common. Finally, the tank's suspension was unsuited for the Scandinavian landscape.
Unlike the Renault FT, the tank was not scrapped, but survives to this day. Nevertheless, KAF gave up on buying foreign tanks. The Swedes decided to build their own tank. Work began in 1928. Since there were no engineers with tank building experience in Sweden, experts were found abroad.
During WWI, Austria-Hungary possessed excellent domestic artillery, which could not be said about its armoured vehicles. Some success was had in the building of armoured trains, but Austria-Hungary's road vehicles were limited to Romfell armoured cars and Günther Adolf Burstyn's tank project. Like Germany, Austria and Hungary were prohibited from designing and building tanks, and were limited to "training" armoured cars. This was more of a preventative measure, since tank design didn't get too far in the collapsed empire, but there was one man in Austria who managed to create a decent armoured car.
Panzerauto M.26, one of Fritz Heigl's armoured cars. It's not impossible that the creator himself is present in this photo.
Fritz Heigl, the man already mentioned in this article, is known to tank history enthusiasts as the first man to create an encyclopedia of tanks. A much smaller circle of people knows that Heigl was not just a theorist, but also dabbled in practice. The "training" armoured cars that Austria was permitted to have were designed by him.
Heigl was 32 years old when he designed his first armoured car, the Panzerauto M.25. He designed three variants of this car, which had a different design of the armament, hull, and chassis. The lighter Heigl Panzerauto M.26 followed. Aside from everything else, Heigl's armoured cars had a very unusual camouflage pattern.
The designer could not develop the success of his design in Austria. The Treaty of Versailles tied his hands, but there was the option to try and seek success abroad. Heigl picked the Swedish Morgårdshammar AB company as a partner and industrial base. Some authors call it an arsenal, but that is incorrect. Morgårdshammar was mostly involved with heavy equipment, including mining equipment and excavators. With this kind of specialization, tank building was a very likely successful offshoot.
47 mm gun designed for the prospective tank.
The first contact between Heigl and Morgårdshammar was made in 1925, but the negotiations reached the practical stage closer towards the end of 1927. In January of 1928, Heigl, already a Major, arrived in Stockholm. Judging by the correspondence, he already had some conceptual designs for his own tank. Sweden also received blueprints of the Heigl Panzerauto M.26. It's worth noting that Heigl did not abandon his country to work on tanks in Sweden. He actively tried to assist tank building in Austria. In 1928, he proposed the creation of a centre for military research in Vienna, but the military refused. Sweden was the only place where the engineer could bring his ideas to life.
SV A1, the Heigl's first draft project. This was an advanced tank for its time.
According to documents, Heigl began with a 9 ton tank. The armament was discussed in February of 1928. Various weapons were proposed. One of them was the Bofors 57 mm Küstengeschütz m/16 coastal defense gun. A 47 mm gun from the same company was also considered. A 37 mm Skoda infantry cannon was also considered, the same one that was to be installed in the Strv m/21.
Finally, the choice was settled for the happy medium: the 47 mm Bofors gun, based on the Hotchkiss design that was later installed into the Renault D1. Unlike the French, the Swedes hid their recoil mechanisms inside the tank, which made the gun less vulnerable to enemy fire. The gun could penetrate 25 mm of armour from 400 meters, which was enough to combat most tanks of the time.
Comparison of the SV A1 and other tanks. These "shadow diagrams" will later appear in Heigl's encyclopedia.
Heigl's first draft project, named "Variant A" or SV A1, was presented in mid-April of 1928. The vehicle was quite unusual, unlike any other tank of the time. It had two command posts, and the presence of a steering wheel implied a complicated transmission (it was not specified in the design). Several layout variants were proposed, two of which had the engine in the front, and at least one in the rear. In any case, the crew consisted of 4 men, and the mass was 10.5 tons.
The 85 hp Scania-Vabis 1561 engine from the Scania-Vabis 324 truck was to be used. An alternative was the Maybach-Omnibus-Motor 100 hp engine. The tank's top speed was estimated at 25 kph, which was enough for the time. The tank had impressive armour: 20-30 mm thick, practically shell-proof at the time.
Variant B with a deployable wheeled drive.
The armament was placed in an unusual way. The gun was located in the turret, and judging by the mount and the shoulder stock, it could be aimed vertically and horizontally without traversing the turret. This was done to make precise aiming easier. An AA gun was present in the rear of the turret. The commander also had a machinegun in a small cupola on top of the main turret. Another machinegun was located in the hull, and would be used by the gunner in an emergency.
Layout of the redesigned tank.
The results was an unusual but satisfactory vehicle. However, a radically reworked "Variant B" project was ready in the second half of April. The crew composition, armament, and engine remained the same, but the tank itself looked different. It became shorter, only one turret remained, and most importantly: it gained a wheeled drive. Using hydraulics, the tank could switch to wheels. The second variant could also move on railroads. In his memo, Heigl noted that the wheels could be used in different ways. They could be used as fascines or help when crossing wide trenches.
Demonstration of the advantages of additional axles. They could help with movement in difficult conditions.
KAAD (Kungliga Arméförvaltningens artilleridepartement, the Royal Army Department of Artillery) viewed these projects with some scepticism. In November of 1928, the Chief of Staff Carl Gustaf Hammarskjöld initiated a new tank purchase program. A decent amount of money was allotted: 400,000 kroner. According to Sweden's requirements, the tank must not be heavier than 12 tons, and its armour must protect from the 37 mm infantry gun. The tank also needed to have powerful armament and the ability to confidently drive along difficult Swedish terrain. Development of the tank had to be done on a tender.
Stridswagen A-4-C, Heigl's last design.
According to Swedish historians, Heigl designed six variants of his tank between 1928 and 1930. The last of them, Stridswagen A-4-C, was dated August 1930. The tank had a lot in common with the "Variant A". The engine was in the front, and the transmission in the back. The turret was also very similar. The machinegun cupola returned. Overall, the tank was somewhat obsolete, but still satisfied the Swedish army's requirements.
Alas, it remained on paper. Major Heigl died on December 30th, 1930, due to issues with his liver. He was 37 years old. The project was orphaned after his death. Morgårdshammar AB had no one who could see it through to the end.
No wheels is better
As mentioned above, the Swedish military declared a tender for a new tank for its army. Heigl's first competitor was AB Bofors. It was essentially a front for the German Krupp conglomerate, which was working on its Leichttraktor at the time. Two prototypes were racking up mile after mile at Kazan, earning many criticisms regarding their design. The Leichttraktor lost the Swedish tender in absentia. In the winter of 1931, KAF reviewed information about the vehicle, and came to the conclusion that the tank is not suitable for Scandinavian terrain. These conclusions were founded, since both the Leichttraktor Krupp and Leichttraktor Rheinmetall were dead ends for the German tank building industry.
Reworked Landsverk L-5 project, without wheels. It served as the starting point for the development of the superior L-10 tank.
The second bid came from Heigl's main competitor, left all alone after his death: Landsverk from Landskrona. It specialized in train cars, dock cranes, and agricultural vehicles. The company also had ties to Germany. In the 1920s, when it was near bankruptcy, the company was bailed out by Gutehoffnungshütte, Aktienverein für Bergbau und Hüttenbetrieb (GHH). Beginning in 1928, Landsverk began to slowly gain footing in a new field: military vehicles. This was not a coincidence. GHH, which also owned MAN, used the Swedish company as a test lab.
Otto Merker began working in Landskrona in 1929. The 30 year old engineer arrived from Maschinenfabrik Esslingen. He designed a tracked and wheeled chassis at his previous job. Allegedly, it was a tractor, but in reality, it was the chassis for a convertible drive tank. Merker's first project at his new job was convertible drive tank. Effectively, it was a rework of the Räder-Raupen-Kampfwagen M28 GFK chassis, more of a German tank than a Swedish one.
The first variant of the L-10, equipped with a simplified suspension.
The result of Merker's work was the convertible drive Landsverk L-5 tank, which deserves its own article. Even though Merker's job was to create a convertible tank, he presented a parallel project: an improved Landsverk L-5 without wheels. The turret and armament were taken from the convertible drive project, as was the engine and suspension. The vehicle's hull was wider, but the overall width was less than that of the convertible drive tank. The protruding wheels noticeably increased its width.
After ditching the massive wheeled drive, Otto Merker was able to improve the tank in other ways. The fighting compartment was larger, and the freed up mass made it possible to reinforce the armour. The convertible drive tank had issues in this respect, since it didn't meet the customer's criteria for protection.
First variant of the L-10 hull.
The delays in work on a second generation tank made KAAD's leadership worry more and more. In January of 1931, Lieutenant Erik Gillner and Captain Walter Elliot (head of the A9 directorate, responsible for motorization of artillery) arrived in Great Britain. They were shown the Medium Tank Mk.IA, Medium Tank Mk.II, Medium Tank Mk.III, and Carden-Loyd Mk.VI tankettes. The result of the trip was the purchase of two tankettes: Mk.VI and Mk.V. Both of them survive to this day.
The Swedes also looked at the Vickers Mk.E and Carden-Loyd Patrol Tank Mk.VI. The military cared little about supporting domestic industry. Nevertheless, the L-5 was given a chance, especially since, unlike Heigl's and Bofors' vehicles, it existed in metal.
Otto Merker's first purely tracked tank was built in metal.
On July 30th, 1921, KAAD was presented with the Landsverk 10 (later L-10) project. The tank transformed noticeably since the improved L-5. The hull was almost half a meter longer, the suspension was reworked. The turret changed, and now resembled the one used on the German Leichttraktor. The engine was also German: the 150 hp Maybach DSO 8. It was considered for installation in prospective German tanks in the mid-1930s, including the B.W. There was also an alternative: the 160 hp air cooled Argus A.S.10W.
The tank's top speed was estimated at 35-40 kph. The Landsverk L-10 was designed in two variants: with 8-14 or 14-24 mm of armour. In the first case, the tank weighed 9 tons, in the second case: 10.5 tons. The tank was armed with a 37 mm Bofors gun and two ksp 6.5 mm m/14-29 machineguns: one coaxial, one in the hull.
The same tank from the rear.
On October 16th, 1931, a contract for production of four tanks was signed. The overall budget was 505,780 kroner. Of that, 343,500 kroner was for three L-10 tanks, or 114,500 kroner each. By 1931 prices, this was a little less than 6500 pounds Sterling. It's not surprising that the KAAD was looking at the Vickers Mk.E. The British tank cost 1.5 times less.
A batch of three tanks was a victory for Swedish tank building, albeit a small one. The Strv m/31 was the first Swedish built tank accepted into service.
The contract did not mean that the tank would appear quickly. Unlike the L-5, which was effectively a polished version of an existing chassis, the new tank was built from scratch. The military did its part to slow down the project, requesting that certain changes be made. One of them was the installation of a radio, which made adding a rail antenna necessary.
The second Strv m/31 crossing an obstacle.
The tanks were delivered to the customer in 1935. The L-10 became the first Swedish tank to be accepted into service and built in a batch of more than one. The tanks were indexed Strv m/31. It's hard to call the tank poor. At 11 tons, the tank reached a top speed of 40 kph. It was no Christie tank, but this was enough to support infantry. Other tanks of this class had the same mobility at the time.
The tank was equipped with a planetary transmission, which was a major achievement at the time. The armament was adequate, and the crew felt very comfortable in its tank. This was a worthy light tank, closer to medium tanks in some respects.
Strv m/31 on exercises. The tank turned out to be quite comfortable to work with.
Despite satisfactory characteristics, no further orders for the Strv m/31 followed. Several factors influenced this decision. The tank was rather expensive, and it was not hard to find a cheaper one abroad. The suspension, unified with the L-30, was complicated, especially the elastic elements, which combined coil and leaf springs. Aside from four main road wheels, there was a smaller one in between the bogeys. The result was complicated and archaic.
Otto Merker did not sit still, and continued to work. In addition to the L-10, he produced the L-100 scout tank and L-60 light tank. Started with the goal of making a smaller L-10, the latter grew into a progressive design that overtook its predecessor. This was especially true for its torsion bar suspension. It's not hard to see why interest in the L-10 waned.
A complicated suspension was one of the biggest problems for Sweden's first tank.
A lack of further orders did not mean that the tanks would do nothing. The vehicles were issued to the Gotaland guards infantry regiment (Göta livgarde, I 2), and received registration numbers 51-53. The tanks earned an ambiguous reputation. They had good off-road performance, but suffered from gearbox issues. Later, two tanks were used at Gotland island as immobile bunkers. The tank with registration number 51 survived to this day. It is complete, and can be seen in storage at the Arsenalen tank museum.
The sad fate of Merker's first Swedish tank didn't mean that it was not an important step for Swedish tank building. This was Sweden's first tank that was accepted into service and produced in any numbers. The overall concept of the L-10 became the foundation for much more fortunate future developments. The L-10 developed into the LAGO export tank, which turned into the Strv m/42, Sweden's most numerous tank of the 1940s. With various conversions, the tanks remained in service until the 1980s.