The deck valve allowing the air to escape from the tanks and the inlets admitting sea-water could be operated by suitable electrical mechanisms, and, once opened, the sea-water would enter and destroy the reserve buoyancy, thus causing the tenders to sink. Again, compressed air supplied from the submarine or compressed air carried by the supply craft themselves could be turned on by electrical control, and the boats brought to the surface at the will of the military commander. 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.