Communist period
After the Second World War, Hungary had to pay substantial war reparations to the Soviet Union, Czechoslovakia and Yugoslavia. A significant part of this was the supply of railway rolling stock, under which MÁVAG delivered 525 locomotives and locomotive parts over a period of five years. This mainly involved the production of standard gauge locomotives No. 122 (the same as the 424 series) (or wide for the Soviet Union), standard gauge locomotives No. 110 (the same as the 375 series) and narrow gauge locomotives No. 70 (the same as the 490 series), but soon afterwards the production of the ЭР series No. 135 was started on the basis of Soviet designs. This became the largest type built by the factory: 1 350 units of the type were built, with the exception of five for the 'big brother'. After the completion of the reparation deliveries, production of the types produced up to that time resumed, now under commercial contracts. The КВ4 series of narrow-track locomotives were also built to Soviet designs.
The main task of the factory's bridge department was to rebuild bridges destroyed in the war.
The factory also made significant deliveries of road vehicles in the second half of the 1940s: 350 Tr5 (so-called "trambus") motor chassis, 95 N5 chassis and 162 B5 trucks. The agricultural machinery division supplied hundreds of T20 and T35 tractors. These products were later transferred centrally to other factories (Csepel Autó and the former Hofherr). Hundreds of locomotives were also produced for the Soviet Union, partly as reparations and partly under commercial contracts.
During this period, the needs of MÁV were very much behind. Work began during the war, but it was not until 1951 that the last locomotive of the factory's own design was built, the heavy high-speed locomotive No. 130, which was given the serial number 303 by MÁV. Locomotive No. 303,001 was MÁVAG's 6000th factory locomotive. Only 2 of this type were built, while the 1'E axle layout freight locomotives and 2'D2' axle layout local passenger locomotives based on the 424 series boiler, as well as a E axle layout shunting steam locomotive, were not built at all, on the grounds that they had to be replaced by diesel locomotives. This decision may be considered premature in today's terms, as the development of diesel and electric locomotives was very slow and this caused a serious shortage of traction vehicles at MÁV by the 1960s.
MÁV was only able to obtain new steam locomotives in significant quantities from 1955 onwards, and these were the long-established 424 and 375 series steam locomotives. The production of the former type was completed in 1958, while the last steam locomotive produced in Hungary, No. 7578, No. 375,1032, left the factory in March 1959, under a new name and organisation (see below).
The factory's first post-war electric locomotive was a five-axle phase and frequency converter locomotive, factory type VM10, of which 12 were built between 1950 and 1957. Mainly due to the backwardness of the back-engineering industry, they were built with a constant delay and operated with low reliability.
A type programme was developed for the design of diesel locomotives. The first of the 600 hp, heavy shunting and light line diesel-electric locomotives of the DVM2 factory type was completed in cooperation with the Ganz factory by the end of 1954 and was given the track number M424,5001 at MÁV. This type was produced from 195 onwards under the serial number M44 and was a great success. The first of the 450 hp diesel-hydraulic shunting locomotives, designated DHM1, was completed for the Egyptian railways in 1957. This type initially caused a lot of headaches and even a loss of prestige for the two factories because of the diesel engines' faults. Even worse was the only heavy main line locomotive, the M601 series, also built in 1957, which was never put into series production because of the diesel engine.
Since the industrial policy of the time decided to discontinue steam locomotive production and to develop diesel locomotive production vigorously, it did not seem advisable to operate the MÁVAG plant, which produced the vehicle structure, and the Ganz plant, which had been nationalised in the meantime and was responsible for the mechanical equipment, as separate entities, and thus to merge the two plants, which were already located in close proximity to each other: thus, from 1 January 1959, the two plants continued to operate as one company under the name Ganz-MÁVAG Locomotive, Wagon and Machine Works.