The supply boats, like the fighting submarine, would have diving compartments, but these would be arranged so that the bottom door could be opened from the outside by divers, who, by manipulating suitable valves, would fill the chambers with compressed air and thus permit the door to be opened and allow entrance into the tender. An air-lock would then facilitate a passage into the inside of the craft, where stores would be stowed. This air-lock would have to be operated each time materials were brought into the diving chamber for transfer to the submarine.
The provisions and other portable supplies would be packed in metal cylinders capable of keeping out the water at any depth in which a diver could work safely. I should count upon carrying on this transfer of provisions, etc., on depths of one hundred feet and less, but deep enough to constitute a sufficient cover against detection by aeroplanes. To facilitate disguise in clear water the tenders could be painted mottled colors which would make them blend into the background of the sea-bed, much after the fashion of a flounder.
These provision tanks, when loaded, would have a negative buoyancy of only a few pounds, just enough to make them sink, and a diver would have no trouble in either carrying or dragging one of them from the tender to the open diving compartment of the submarine. Only food, drinking water, the ammunition for guns, and the disjointed sections of torpedoes need to be transported in this way. Fuel oil for the engines, and even lubricating oil, could be sent from the tender to the submarine in a very simple manner. The outboard connection of the oil tanks of the supply craft would have hose joined to them leading to the fuel tanks of the submarine, and the contents could be transferred simply by pumping them across.
The supply boats should have fenders in the shape of long metal rods reaching out from the bow and the stern and both sides. These would give the tenders the appearance of gigantic water-bugs, but they serve to form smooth surfaces over which the loop of a mine sweeper would glide freely without encountering any projections to which it could cling. Thus, while the mine sweeper could certainly pick up a floating mine, it would pass without warning over a submerged supply base capable of holding stuff sufficient to keep a submarine going for weeks without return to her home port.
With such a system of revictualling, submarines should be able to operate secretly for long periods and virtually hold to the sea during the entire time, doing in that interval what would be absolutely impossible for any type of surface fighting craft of kindred displacement and military power. The submarine commander would be the only one having knowledge of the position of his submerged supply bases, and he could place them under cover of night just where they would contribute best to the carrying out of the operations planned for him.
SUBMARINE "SEAL"—LAKE TYPE U. S.
This vessel is unique in that she was the first vessel built that was provided with deck torpedo tubes that could be trained and fired to either broadside when the vessel is submerged, in addition to the vessel's hull tubes. In her acceptance trials her crew took her down to a depth of 256 ft. She broke the record for speed in the U. S. Navy.
On almost every coast there are areas where submarines could sink safely to the bottom in moderate depths of water, and there are also quiet coves but little frequented where ideal resting places could be found for the submerged supply boats. With these failing, however, the tenders could be sunk to the water-bed in the open sea, and with their bottom wheels to rest on, working upon pneumatic buffers, they need not feel any vertical motion of the sea even in the stormiest weather. I have found that such motion actually exists forty feet and more below the surface when the ground swell is deep.
