The Sv12 is a diesel-hydraulic road locomotive built by Valmet and Lokomo between 1964 and 1984. It has bogies from the German V160, which can be switched between a top speed of 85 and 125 km/h. A version with an additional steam generator for passenger trains was called Sr12. After the steam generator was removed due to lack of demand, both variants were referred to as Dv12.

Since the installed power of 1,000 kW became too low over time, the locomotives are now mostly used double or triple headed. From 1978, No. 2501 was converted into an electric locomotive with 1,100 kW and tested in this form for four years. Since most of the main lines in Finland are now electrified, retirements began in 2009 and the remaining locomotives are now mainly used on branch lines and in shunting services. The diesel-electric, twin-engine Dr19 is currently being introduced as a successor on non-electrified lines.