Like their forebears that have plied the Wisconsin Dells for decades, these 75-minute tours are conducted in clumsy, American-made DUKW amphibious vehicles, which roll down streets like buses and then plow into the Thames and motor along briefly as boats. Roofed and mostly splashless, these vehicles were developed as Word War II transports. You can’t hop off and you only see Whitehall, Westminster, and Vauxhall. A 2013 fire incident kept them running only through mid-2014, but safety changes have satisfied the government and by 2015 they will be plying the Thames again.