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In this field, it was decided to use American industry to fulfill an order for 100 locomotives. 

As of May 1, 1947, sixty-six of them had arrived in France.

The purpose of this note is to present the essential characteristics and certain particularities of these locomotives. 

At the time when the calls for tenders were launched, the United States industry was governed by the war economy. In these conditions, it was not possible to think of building French-designed diesel locomotives; moreover, it was interesting to take maximum advantage of the already long experience acquired by the Americans in this field. However, from the first contacts between the members of the French Mission of the SNCF and the representatives of the American manufacturers, it became clear that the acquisition of locomotives of a standard American type was impossible, our tracks and our structures not being able to support the axle loads, of the order of 25 t, commonly accepted across the Atlantic. It was therefore necessary to develop a locomotive project adapted to the French network, but whose constituent elements would be chosen from standard American components. 

The project finally chosen derives from the American locomotive BB of 1,000 hp, of the "Road-Switcher" type, used for marshalling services (by throwing or by gravity) and line services (local trains, reinforcements, emergency trains). But, in order to reduce the axle load to less than 18 t, the 2-axle bogies were replaced by 3-axle bogies, the middle axle being simply carrying; it was thus possible to keep the same types of electric motors, therefore the same standard electrical equipment. In addition, the S.N.C.F. intended these locomotives exclusively for shunting services, the power of the Diesel engine was reduced to 660 hp only. by adopting the 6-cylinder engine instead of 8, while the boiler used for heating passenger trains was removed. 

The adoption of this solution safeguarded the major interest of rapid delivery, guaranteed that the service provided would be satisfactory. thanks to the large safety margin achieved. finally provided a very opportune opportunity to judge the value of this American equipment which had proven itself, both in the U.S.A. and in the main theaters of military operations, particularly in Iran, where extremely severe operating conditions had led to the abandonment of steam traction. It also made it possible to adopt American maintenance methods without serious risks.

Two equally experienced manufacturers, the American Locomotive Company and the Baldwin Locomotive Works, responded to the SNCF's calls for tenders; their solutions and prices were equivalent, but the Baldwin Locomotive Works' proposal was ultimately chosen because they were able to deliver within shorter timeframes. An initial order for 30 locomotives, to be built under "lend-lease", was supplemented by a second order for 70 units acquired under the Export-Import agreement.


GENERAL CHARACTERISTICS

The general characteristics of the locomotives are given in the diagram (Fig. I). 

The frame (see Fig. 2, page 243) is a single piece of cast steel, 17 m long, weighing 23 t, which, along with the truck frames, was cast by the General Steel Castings Corporation, a well-known specialist in single-piece steam locomotive frames. The strength of this frame makes it virtually immune to any damage that might occur in a shunting yard.