That problem may be visualized in the obvious difficulty of maintaining physical contact between an airship and a surface ship. The two move in different media, one influenced mostly by the waves, the other mostly by the wind. The surface ship is moving up and down, the airship subject to gusts which might break the contact or thrust it violently against the masts or superstructure of the surface ship. Servicing has been done under favorable circumstances, but could not be relied on as standard procedure.
The solution reached was this. The pilot swings his ship down to within 100 or 150 feet of the water, lowers a hose with a small bronze scoop, not much wider than the hose, so as to lessen the drag.
Twenty-five feet up from the scoop is a streamlined cylinder, blimp shaped, carrying a small electric pump. This cylinder, nicknamed the “fish”, has tail fins to keep it from spinning, and skims along the surface or jumps out like a porpoise, but the scoop is far enough behind and heavy enough to trail easily beneath the surface, stays directly in the ship’s wake, continues without interruption to pick up ballast for the airship above.
The whole gear weighs slightly more than 100 pounds, can pick up water at cruising speed, can function in rough water or smooth. The Navy J-4, chiefly used in these experiments, normally consumes 500 pounds of fuel in five hours of flying at cruising speed. It was able to pick up that much water ballast in seven minutes.
The next step was to enable an airship to obtain fuel from a tanker or other ship without physical contact or advance arrangements—even from a passing merchantman. The pilot asks by radio or voice whether the surface ship can spare some gasoline, and on an affirmative answer, lowers or drops on his deck two rubberized fabric spheres connected to each other by 14 feet of rope—also a note of instructions. The smaller sphere is an ordinary air-filled buoy, the larger, about three feet in diameter when filled, is the fuel bag. The surface ship fills the fuel bag, then drops both bags overboard, being careful only that they do not get tangled up. Then the airship flies over the two bags, drops a hook between them, hauls away, pumps the gasoline into its tanks.
The third device permits an airship to anchor in the open sea near a surface ship to transfer crews or take on fuel and supplies. The anchor is a cone-shaped rubberized fabric bag, ten feet long, with a diameter of 2½ feet at the top. It is lowered 50 feet below the airship by two cables connected with each other by rungs to form a ladder. Half of the cables’ length is made up of heavy exerciser cord to dampen the effect of wave movements. On top the cone is a wire mesh cover which allows the water to pass through, and is strong enough to act as a platform, supporting a man.
As the cone fills up the airship drops ballast till its “mooring mast” is half submerged. The principle of the drag rope comes into play—if the airship starts to rise it finds itself lifting an increasingly heavier load, counteracting the rising tendency. If it starts to settle down toward the water, the load is correspondingly lessened and the ship grows lighter. The result is that the airship is held highly stable, even in a rough sea. The surface ship then sends a small boat alongside and dispatches the relief crew members or supplies, them up and down the ladder, or uses a winch, the platform atop the anchor serving as the operating base. This system also permits the moving of a sick passenger ashore, or the rescue of a man overboard.
When the airship is ready to leave its anchorage, the cone is tipped by a line attached to the bottom, spilling the water, and hauled aboard. The servicing ship need carry no special equipment. The weight of cone and ladder is negligible.
By being able to pick up ballast and borrow fuel from a passing ship, (neither airship nor surface ship need slow down for the fuel exchange if going in the same direction) the airship greatly increases its radius of operations.
The advantage of being able to change crews at sea may not be quite as clear. This, however, grows out of the fact that today’s non-rigid airship has greater endurance than the crew which flies it. An anti-submarine, anti-mine patrol calls for constant alertness. Reduction of vibration and noise, the use of closed cars instead of open cockpits has lessened fatigue, enabling men to remain on duty over longer periods than before. But obviously there are limits.