An amphibious platform vehicle-vessel to support and to move hydraulically operated and controlled earth-moving and lifting equipment, such as excavators and cranes, on solid ground, semi-solid or marshy ground, shallow water, and deeper water. The modular units can be transported to a worksite on separate trailers and assembled and reconfigured on site. Two compartmented pontoon units are mounted to an adaptive cross member that can accommodate different types of moving-lifting equipment through different mounting flanges, and to auxiliary cross members. Propulsion is provided through amphibious cleats on drive chains in chain tracks driven by dual-motor driving drums and over a tension-adjusting passive chain roller, surrounding a sealed pontoon shell internally reinforced with bulkhead partitions, beam shell-bottom stiffeners, and pressed-angle shell-bottom stiffeners. An extendable auxiliary float can be extended outward from each compartmented pontoon for increased stability in floating operations.