A great decision be take with middle of the Thirty with the setting in building site of a machine of replacement of class S14, under the form of a Pacific with two cylinder simple expansion and distribution by valve, classify class S16. The study be carry out of concert by the OCEM and the SACM. Two prototypes, the 1401 and 1402, are built in Graffenstaden. Built on a frame out of bar with a suspension combined similar to class G12 having given excellent results, the three coupled axles have a diameter of 1m95, an interior member bogie and combined suspension, carrying axle AR on which is mounted an engine with vapor with two pistons having to allow takeoff without difficulty of the heavy oars. This apparatus, called ' Booster' or engine auxiliary of use in the USA, is not assembled on the 1402 in order to compare and to evaluate its effectiveness. Another innovation relates to the driving part: the two cylinders simple expansion 575 mms in diameter for the 1401, with 540mm for the 1402 are equipped with the distribution with Caprotti valves. This one functions in the following way: to the medium of the hub of the first coupled axle is attached one limps with gears which make it possible to transmit a rotary movement to a camshaft laid out between the blocks cylinders and driven by another gears at the end of the reference. The rotation of the cams allows the opening and the closing of the valves which ensure the phases of admission and of exhaust the place of the lights of the drawers which are of this fact non-existent on such machines. Outside, the distribution is limited to the stem of piston, stick and slide, the rods motor coach and of coupling. The personnel of the network is not long in finding the nickname of ' Kougelhopfmaschine' to them while having made the bringing together between the shape of the valves in their housing and that of the cake pan intended to cook a great Alsatian speciality: Kougelhopf. During a great repair to the workshops of Bischheim, Al chooses P8 2365 to be equipped with the Caprotti distribution in order to test this one; 120.000 kilometers are then traversed without incidents nor opening or disassembling of the mechanism. The boiler, also inspired of G12, consists of rings out of steel or nickel and has a hearth largely overflowing, carried out in a a little preserving way out of copper. The Belpaire hearth was not retained in order to free itself to the maximum of the spacers and ties. The wicket of the hearth is driven by a pneumatic control. The smoke-box is lengthened to place the Schmidt superheater conceived for the very large machines and has a double chimney. The column of exhaust is divided into two and is surmounted by two Kylala conduits - name of its Scandinavian inventor, on the top of which are suspended two called reversed funnels ' American Peticoat'. This combination imagined by André Chapelon, known under the name of exhaust ' Kylchap' is in the beginning intended to restore sufficient violence to the overdrawn exhaust of the engines compound to four cylinders because of the outgoing vapor too slackened of the LP. On an engine with simple expansion having an exhaust ' sain', the effects of this apparatus are nevertheless less beneficial. The boiler is supplemented by a dome containing the valve regulator imprisoned in a common envelope with the sand pit - provision also inspired of G12. A compressor Bi-compound on the left, a pump ACFI on the front cross-piece, heaters on both sides of the chimney (certainly the most unaesthetic element of these beautiful engines). A cabin has two windows including one sliding. The 1401 receives screens of a a little old drawing, but the 1402 is equipped with Wagner screens, larger and more effective, which will involve soon the modification of those of the 1401 per addition of sheet elements to the AV and with AR. A tender with the very modern drawing assembled on two bogies, of 28 m3 water and coal 8t of which the spillplate correctly releases the sight backwards, is coupled.