During the latter stages of World War 1 (1914-1918), the Germans were working on a light tank design to be used in infantry support actions. The effort was headed by Joseph Vollmer and began with the Leichter Kampfwagen I (LK I) which appeared in two prototype examples by June of 1918. These were to served solely as the basis for the upcoming production-quality "LK II" which was armed with a 37mm cannon and ordered in 580 examples. However, the end of the war in November of 1918 put an end to this order as well as further work on the type.
In the post-war years, the government of Sweden secretly ordered components for ten of the LK II tanks and these arrived in-country to be assembled under the designation of "Stridsvagn m/21" (Strv m/21). The initiative began Sweden's long-running local tank history which continues to this day. Unlike the cannon armed LK II vehicles of the Germans, the Strv m/21 was outfitted with 2 x 6.5mm Madsen ksp m/14 machine guns. Its combat weight was 9.7 tons and length was 19 feet with a width of 6.7 feet and height of 8.3 feet. Road speeds peaked at 10 miles per hour. Another change was the addition of a fourth crew member.
The original German tank was based on a Daimler automobile with an armored superstructure simply added over the existing chassis. As such, the internal configuration mimicked that of a traditional automobile arrangement with the engine held in a forward compartment, the driver over the middle, and a passenger seating area at the rear. The two axles were retained though now mounting track idlers and drive sprockets instead, these driving a track-over-wheel arrangement at the side of each hull. An angled hull superstructure was fitted over the rear portion of the car and this encompassed the driver's position and fighting compartment for the three-man crew. A turret was installed over the compartment and was used to manage the primary armament.
In 1929, five of the original batch were rebuilt into refined forms, chief among the changes being the installation of a 37mm main gun. An alternative version carried two machine guns instead but both became powered by the local Scania-Vabis gasoline engine over the original Daimler-Benz 4-cylinder. Armor was also revised for improved protection but the same general lines were retained. The work begat the updated "Strv m/21-29" designation used to cover these vehicles.
The culmination of this early became the Stridsvagn m/31 of 1931 - also known as the "L-10" - which came from AB Landsverk and appeared as a very modern light tank for of the 1930s. It continued use of a 37mm main gun but the turret was now positioned more forward as seen in contemporaries. By this time, the German government managed a share of the company and added assistance to Sweden in design, development, and production of their first true indigenous tank. The line then continually evolved during the war years until the m/42 of 1943 which was the first Swedish tank to utilize a 75mm main gun.
The m/21 and m/21-29 tanks remained in service from 1922 to 1939, just prior to the fighting of World War 2 (1939-1945). Only the ten were ever procured but proved monumental in helping to solidify a local Sweden tank industry which continues today.