The thing is the carriage car for the French 240mm Gun Mle 1903, i found the following info in Allied Artillery of WW1 by Ian Hogg..............Fom the book "The vehicle was fitted with four wheels of standard gauge plus two narrow gauge four wheel bogies,one at each end of the car ,For normal running and covering major journeys it travelled as a standard gauge hehicle as close to its firing site as could be arranged.After that it could be jacked onto a set of road wheels and pulled by a traction engine,or shifted onto a narrow gauge track by lowering the narrow gauge bogies by means of screw jacks.It was then run into its firing position,which was a prepared bed of earth and timber through which the narrow gauge track ran.Once the car was straddling this bed the jacks were used to lower it into a firm contact.In order to lighten the equipment when travelling by road or narrow gauge ,the gun could be lifted from the carriage to a separate transport car,this was done by a large A-frame with lifting tackle pemanently fitted to the carriage vehicle.All in all this was a very complicated piece of equipment which involved a great deal of hard work to get into place,once emplaced it was satisfactory enough.However ,relatively few appear to have been built"