The L-35 was designed in the late 1920s on the request of the Finnish Army, who sought to develop an indigenous arms program. The initial L-35 prototypes were chambered in 7.65×21mm, however by the time full production began in 1935, a decision had been made to switch to the 9×19mm cartridge, which was more widely available and also used by the Finnish KP/-31 submachine gun.
Initially, production of the L-35 was very slow, with only 500 models being produced by the time of the Winter War of 1939. Production ceased as a result of the conflict, and did not resume until the beginning of 1943, upon which progress came along quicker and a further 4,500 pistols were produced. In 1944, however, production was stopped once again, as Finland's economy was strained by the effects of World War II.
After the war, in 1946, the L-35 finally re-entered steady production, with 12,000 units being produced until 1950. A further 1,250 pistols were made in 1958, by which time the Valtion factory had largely disposed of the machinery used to create the original run and were relying on assistance from the Swedish firm of Husqvarna Vapenfabriks. Husqvarna had produced a licensed copy of the L-35 during the war, known as the M/40.
The L-35 was also offered in small numbers for the civilian market. About 1,000 models were rejected for Finnish Army service and subsequently sold as surplus goods. These models are marked VO. Component kits for the pistol were produced into the 1970s. In 1985, Valmet produced a limited 50th anniversary line of L-35s.
Although the Lahti L-35 heavily resembled the Luger externally, internally it was nothing alike. It did not operate on the toggle-lock principle, but instead was recoil-operated with a concealed hammer, firing from a locked breech. The rectangular bolt was housed in a recoiling barrel extension that receded into the breech of the pistol. Behind the breech was a curved bolt accelerator, an unusual aspect of the L-35's design. This accelerator would be pushed backward upon firing by the force of the recoil, upon which it would spring back and strike the bolt at a high velocity. The bolt at this point would become unlocked and speed toward the chamber.
The bolt accelerator was necessary for the pistol to function properly, as the bolt would have otherwise lost energy due to the long length of the recoil stroke that operated it. This was proven when an early batch of L-35s were built without the bolt accelerator, and subsequently had to be returned to the factory to have it fitted.
The L-35 was fed from an 8-round magazine and cocked by pulling back a ribbed nut that protruded from the rear end. Early L-35s were built with a chamber indicator that would alert the user when the chamber was empty, but this feature was dropped after the first 9,000 models in order to cut production costs. The first 1,000 pistols were built with wooden grips, and all subsequent models were built with plastic checkered grips.
Built to an excellent standard and operating on a reliable mechanism, the Lahti L-35 was, and still is, highly regarded by experts and collectors. It is considered by some to be one of the finest pistols to see military service.
The pistol was built with a sealed frame that was not designed to be stripped without a full set of tools. It should be noted, then, that disassembly of the L-35 should not be attempted without assistance from a trained armorer.