M28 designates a series of small shunters designed by MÁVAG and built by Rába from 1955. They have two axles and were originally powered by a 130 hp Ganz diesel engine. There was a variant with mechanical power transfer and a top speed of 30 km/h that was called M28.1 by the MÁV and another one with a hydromechanical gearbox and a top speed of 50 km/h, called M28.2.

The MÁV received 24 M28.1 and ten M28.2. Around 75 more were built for private operators and called A21. They also got the nickname “Raisin”. Originally used as station pilot and for light transfer services, many are still operating in the 21^st century. But today, they are only used in depots and workshops. In the meantime, many were upgraded with license-built MAN motors which deliver 200 hp. 

To replace the last steam locomotives on secondary lines, the MÁV needed a powerful diesel locomotive with a low axle load. To stay within the weight limits, Ganz-MÁVAG selected hydraulic power transmission, what led to the asymmetric centre-cab prototypes of the type M46. This was not selected for mass production for MÁV, but from it the more powerful, dual-cab M41 was developed.

They got a license-built Pielstick engine with 1,800 hp and a Voith transmission. Train heating was electrically. Between 1972 and 1984, 107 were delivered to MÁV. Additionally, the GySEV received seven more and the Greek OSE eleven. As early as in the eighties, the MÁV rebuilt them with a more modern variant of the original engine and other improvements.

Their importance sunk with the electrification of many lines in Hungary from the year 2000. But between 2002 and 2008, 35 received a modern engine either from MTU or Caterpillar. They received the new class number 318 in 2011, but in 2016, a large number was scrapped. In Greece, the last one had already been withdrawn in 2005.