Oxygen cycle devices are much liked by combat divers and underwater photographers, as they make far fewer bubbles than aqualung-type (open circuit) sets, and those bubbles could betray the diver.
The artist avoided the error found in most comic-strip drawings of old-type aqualungs, of drawing each breathing tube coming directly from a cylinder top and no regulator.
His training gives him many extraordinary talents, i.e. underwater breath control for diving without an aqualung, and a limited understanding of the supernatural.
