War Flats were developed to carry tanks during the latter part of WW1, during WW2 tanks became heavier because of [mainly] thicker armour and bigger guns. This meant that the War Flats were strengthened to carry up to 50 tons.
This little Bren Gun / Universal Carrier weighs 3t 5cwt unladen and you can add up to 11cwt for fuel, armament / ammunition and the crew [They could, apparently, carry supplies in the crew space if needed]