=Unsinkable Ships.=--Unsinkable ships are possibly practical to a limited extent. Numerous proposals of ship construction along this line have been made, mostly of ships built up on the cellular system. Some proposals have also been made for carrying the cargo in hermetically sealed tanks that would assist in floating the ship if she were torpedoed. The objections to the construction of vessels of this class are its enormously increased cost over the ordinary cargo ship, the reduced carrying capacity per ton of displacement of such vessels, and the impossibility of preventing injury to ships of this sort to such an extent as to make them unmanageable. Any surface ship, to meet fully the submarine menace, must be not only _unsinkable, but it must also be indestructible_. When a ship once becomes unmanageable and incapable of getting away, a powerful mine or mines may be placed at considerable depth under her bottom and the whole fabric blown up into the air. [Illustration: CARGO-CARRYING SUBMARINES OF THE AUTHOR'S DESIGN They will carry 7500 tons of cargo on a surface displacement of 11,500 tons; their submerged displacement is about 13,500 tons.] =Convoys.=--Convoying a merchant fleet offers perhaps some safety to the individuals on the ships in case some of them are lost, but I cannot see that it offers much protection to the fleet as a whole, as the speed of the fleet is limited to that of the slowest ship, and the smoke or appearance of the leading ships are more apt to give a waiting slow-speed submarine time to catch up with the tail end of the fleet. If it came to a gun fight the fleet might have the advantage, but in experimental work I have frequently run in amidst a fleet of ships, and their first knowledge of my presence was when the periscope was extended above the surface. As it is only necessary to extend this for a period of a few seconds' duration to get the range and bearing of one of the ships to aim the torpedo, the chance of a gunner getting the range and hitting the periscope is very slight, and, even if the periscope were destroyed, it is easy to replace it with a spare one.