 The Maginot line was built with both external and internal 600mm railways, the former served by combustion engines pulling supply trains from marshalling yards behind the front, and the latter, served by electric locomotives taking over the loaded wagons inside the fortifications.Tracks inside the fortresses went from the munitions entries in the rear all the way up to the fighting blocks, where ammunition loads were transferred to forward magazines using overhead monorails.Similar "feldbahn" equipment was used in German South-West Africa where "Otavi Minen- und Eisenbahn-Gesellschaft" built the gauge "Otavibahn".