The Maybach diesel engines used in the locomotives proved highly unreliable, resulting in a complete overhaul of the engine-transmission system in 1956–58, but this did not solve all of the reliability problems.

VR (Finnish Railways) started a modernization project in the early fifties.

Modern aluminum-carriage diesel powered express multiple units (Dm3 and Dm4) were introduced in 1952.

[1] The locomotives carried a gray livery, with wine-red broad stripes.

The gray color and sleek looks earned it the nickname Lentävä susi (Flying Wolf).