A quadrotor UAV including ruggedized, integral-battery, load-bearing body, two arms on the load-bearing body, each arm having two rotors, a control module mounted on the load-bearing body, a payload module mounted on the control module, and skids configured as landing gear. The two arms are replaceable with arms having wheels for ground vehicle use, with arms having floats and props for water-surface use, and with arms having pitch-controlled props for underwater use. The control module is configured to operate as an unmanned aerial vehicle, an unmanned ground vehicle, an unmanned (water) surface vehicle, and an unmanned underwater vehicle, depending on the type of arms that are attached.