After the express locomotives with the 2-4-0 wheel arrangement could not reach sufficient speeds and the first 4-4-0 locomotives procured could not convince either, the construction of the locomotives later designated as series Ia was commissioned. In most details, they were based on locomotives that had been built for the KFJB from 1879 and bore the numbers 201 to 213. With these, the MÁV was able to operate express trains at a speed of 90 km/h for the first time.
The locomotives had an outside frame, outside cylinders and Hall cranks. The first 16 were delivered between 1881 and 1885 and had a boiler pressure of 10.5 bars. A further 185 were delivered between 1890 and 1905 and had a boiler pressure increased to twelve bars. The Kaschau-Oderberger Bahn procured five identical units from 1895.
In the beginning, the series Ia could be seen in front of the most important express trains. However, the more powerful series Ie was procured while this was still in production, which contested the service of the Ia on the lines originating from Budapest. They were now increasingly used on the connecting lines between the major main lines.
Later, four were equipped with superheaters, which increased the haulage capacity at 90 km/h on the level from 107 to 161 tonnes. However, a general rebuild of the remaining locomotives did not come about and soon they were only used on branch lines. MÁV retired the last ones in 1952. During the First World War, 79 were sent to the CFR in Romania, where they were scrapped by 1945. Six ended up in Czechoslovakia, where they were designated class 264.5 and were in service until 1937. After the nationalization of the KsOd, five of these also came to the CSD and were designated there as class 254.4.
