The ML 2/2 was a local railway tank locomotive that was built by Maffei between 1906 and 1908 as an alternative to the more well-known PtL 2/2 by Krauss. Although it was a very small and light locomotive, it was fitted with a very complicated and difficult to maintain powerplant. The “M” in the designation goes back to the term “motor locomotive” and serves as a reference to the powerplant with opposed pistons. There was a cylinder on each side between the widely spaced axles, the counter-rotating pistons of which acted on both wheel sets with short connecting rods. Inside the frame were the coupling rods that connected the axles.

With this special arrangement, the prospect of a perfect load balancing was presented. The maximum car load at 50 km/h on the level was 65 tonnes. The same load could still be pulled on a gradient of 2.5 percent at around ten to twelve km/h.

Otherwise, the ML 2/2 was designed to be just as suitable for everyday use as other Bavarian local railway locomotives. In order to be able to do without a fireman, there was a dumping device for semi-automatic loading of the grate. Passenger cars could be entered from either side of the locomotive. On a towed train, the gangway consisted of a door at the rear of the cab. However, if the train was pushed, the transition could be reached via a running board on the sides of the boiler. For this purpose, the water tanks were narrow and elongated so that they could be walked past without any problems.

24 examples were built for the Bavarian State Railways, three of which were sold to the firebrick factory in Marktredwitz in 1922. The rest were retired in 1924 because the maintenance of the internal parts of the engine was too expensive. The planned transfer to the Reichsbahn numbers 98 361 to 98 384 therefore did not take place. In 1907, the Hungarian MÁV had two ML 2/2 built under license for suburban traffic in Budapest. In contrast to the Bavarian engines, they had an certified maximum speed of 60 km/h, since the complicated powerplant was expected to run smoother.