 In the latter case, the fuel tank was divided, with half for diesel fuel, and half for boiler water.One option available for locomotives without dynamic brakes, was to remove the two  air reservoir tanks from under the frame, and replace them with four  tanks that were installed on the roof of the locomotive, above the prime mover.These "torpedo tubes" as they were nicknamed, enabled the fuel and water tanks to be increased to each, although some railroads opted for roof-mounted air tanks and  fuel tanks on their freight ‘Geeps’.