Since the various existing types of railcars were not suitable for introduction in large numbers, a standard type was developed at the beginning of the 1950s. Experience from the narrow-gauge railcars of the RALn 60 type was applied here. To save costs, they received two commercially available truck engines, each driving one axle. The class 813 of the JŽ and the Y1 of the SJ were derived from the ALn 668.

787 vehicles were built between 1954 and 1981. They were created in several series, which had, among other things, different engines or different door placement. The railcars were usually used individually, but depending on the series they were also capable of multiple working. Specially developed control cars were rarely used because they were only approved for 90 km/h. The ALn 668 were only replaced by the Minuetto at the beginning of the 21st century.