The 242 AT was the first of four series of 4-8-4T tank locomotives that the PLM had built to accelerate the suburban trains that departed from the Gare de Lyon in Paris. They replaced the tank locomotives 232 AT and 232 BT. A total of three manufacturers delivered 120 locomotives between 1926 and 1929.
They had a Belpaire firebox with a steeply sloped grate between the wheels of the third and fourth driving axles. Power was transmitted via four compound cylinders of de Glehn system. Over the years it often became apparent that the frames were too weak for the long wheelbase.
They were classified by the SNCF as 5-242 TA. After the war, they were distributed across several regions and received region-specific adjustments, for example wind deflectors. They were decommissioned by 1968.