Chemins de fer de ceinture No. 4001 to 4005

After the purchase of the 4-6-0T tank locomotives with the numbers 51 to 65, the Paris belt railway needed even more powerful locomotives which were primarily intended for freight service. The requirements included 550-tonne freight trains on one percent and 430 tonnes on 1.5 percent. At times of high passenger traffic volumes, additional passenger trains were to be hauled.

This time again tank locomotives with a front bogie and without trailing axles were ordered. The five locomotives therefore had a 4-8-0T wheel arrangement and a four-cylinder compound engine. While numbers 51 to 65 were tandem compounds, the new ones were De Glehn compounds which were common in France. The high-pressure cylinders were on the outside at the height of the rear axle of the bogie and drove the second driving wheel set, while the low-pressure cylinders were inside the bogie and drove the first driving wheel set.

Since all the cylinders were inclined and mounted higher up and the water tanks started behind the bogie, easy accessibility of the cylinders for maintenance was ensured. The leading bogie enabled them to move passenger trains at 70 km/h without sacrificing smooth running. The ability of the coupled axles to negotiate curves was realized by weakening the wheel flanges of the second and third axles and without side play in axles.