Aimo Lahti was the premier firearms designer, and the m/26 was his first significant design. Lahti was a Civil Guard armorer, and upon seeing the Lindelof copy of the Bergmann SMG in 1921 he thought he could make something better and cheaper. He took on three partners and formed Konepistooli Osakeyhtio (Submachinegun Limited) and spent several years developing his design. It was chambered for 7.65mm Parabellum, with a large curved 36-round magazine, a safe/semi/full selector switch on the side of the receiver, and a theoretical rate of fire adjustment based on air compression behind the bolt (which didn’t really work). They sold a few guns to the Finnish Army in 1924 for testing, and a few addition small batches in 1925. Only about 100 were made in total, and these sales were barely sufficient to keep the company afloat financially. Ultimately the design was improved to the m/31 pattern, and the original four investors sold their rights in the company and gun to Tikkakoski for a nice cash payment plus royalty per gun produced. Tikkakoski would produce the m/31 for the Finnish Army and several export companies throughout the 1930s and early 1940s.
Thanks to Sako for giving me access to film this very rare example from their factory collection!