In order to increase standardisation, and to reduce operating and maintenance costs, the 5.1200s shared many parts with the third series of Super Pacifics (3.1251 to 3.1290) and the suburban Mikado tank locomotives (4.1200 to 4.1272).
[1] The class was built between 1933 and 1935 by the Nord's workshops at La Chapelle and Hellemmes-Lille.
The 5.1200s had the same boiler as the Super Pacifics; the Belpaire firebox was riveted and made of copper.
[2][3] Originally, they were hand-fired, but the coal consumption was such that in 1934, 10 locomotives of the class were fitted with mechanical stokers.
After nationalisation in 1938, the SNCF livery – No.306 exterior green and black with yellow lining – was gradually applied.