The K5, also called “Pikku-Jumbo” (“Small Jumbo”), was the largest class of steam locomotives ever in use with the Finnish State Railways. It is also known by its new class designation Tk3 introduced in 1942. It was a 2-8-0 “Consolidation” designed for freight and passenger working on light tracks and therefore it had an axle load of only 10.7 tonnes. As usual in Finland, it was designed for coal and wood firing and had a balloon stack. Production of these 161 locomotives went on over a long time.

The first 100 were built by Tampella and Lokomo between 1927 and 1930. Two more, which came to the VR on nationalization in 1950, had been built for the Rauma Railway in 1927 and 1935. After 24 had been given to the Soviet Union in 1940 after the Winter War, production was restarted in 1943. Due to the war conditions, only 35 had been completed by 1948. So 20 more were produced by Frichs in Denmark in 1949. The last four again came from Lokomo in Finland in 1953. Withdrawals started in the sixties and were only completed with the end of steam in Finland in 1975.