The VR took into stock a light compound engine designed for mixed traffic when the private Raahe Railway was absorbed in 1926. This locomotive, built by Tampella in 1908, entered service with the VR as number 401 and classified G11 but was reclassified as G12 and renumbered 67 in 1927, and class Sk5 in the 1942 reclassification scheme. It spent its days on the VR system at Oulu locomotive shed until it was purchased by the private Rauma Railway in 1948. However, this locomotive was regained two years later with the incorporation of this private line into the VR and its former class designation and number were restored. Another identical engine, but built for the Rauma Railway in 1912, was also taken into VR stock in 1950, being designated Sk5 class no. 66. The VR had actually temporarily employed this engine in 1918 when the Tampere–Pori line was damaged during the Finnish Civil War.
The G12 was an improved version of the various Moguls that eventually became classes Sk1 and Sk2. This two-cylinder compound engine with bar frames was fitted with a saturated steam boiler using a steam pressure of 12.5kg/cm2 and, typically for that era, Stephenson inside valve gear with slide valves was used. The G12 had a greater tractive effort than the Sk1 and Sk2 classes on account of its higher boiler pressure and fractionally extra weight. Its four-wheel tender was slightly larger than the type used by the Sk1 and Sk2 classes. The VR converted the G12s for wood burning and equipped them with carbide gas lighting.
This pair of engines was used by Tampere depot from 1950 until their withdrawal in 1953 and 1955.