 The "bobbin" tank would overcome this problem by deploying a roll of matting over the soft surface and leaving the material in place as a route for more conventional tanks.The Armoured Vehicle Royal Engineers (AVREs) were modified for many tasks, including laying bridges and firing large charges into pillboxes.The Duplex-Drive tank (DD tank), another design developed by Hobart's group, was a self-propelled amphibious tank kept afloat using a waterproof canvas screen inflated with compressed air.