I have been informed by one naval architect of standing who investigated this phase of the problem that nets of sufficient strength to protect the sides of a ten-knot ship from a torpedo attack cut the speed of the ship from ten knots down to two and one-half knots per hour. It would therefore take a ship protected in this way four times as long to make her voyage; her chance of discovery would therefore be four times as great and her chance of destruction, if once discovered, be almost certain, as a submarine could readily overtake her and plant mines in her course or even tow a mine underneath her bottom and explode it there, which would destroy the ship much more completely and quickly than a Whitehead torpedo exploded against her side. Devices have also been developed which enable a torpedo to dive under a net and explode under a ship's bottom by a slightly delayed detonator.
Torpedoes have also been built with net-cutting devices, and they have been known to penetrate a ship's plating and sink the vessel without exploding. It is not an easy matter to stop a projectile weighing nearly a ton speeding at thirty-five or forty miles an hour. I can see no hope in stopping the submarine menace by any device in this class.
Magnets.—Some proposals have been made to divert the torpedo by powerful magnets extended out beyond the sides of the ship or at the ends—on the theory, I suppose, of fishing for little fish in a pan of water—the Whitehead torpedo being built of steel in this country and England. It is not generally known that the Schwartzkopf torpedo built by the Germans is built of bronze, or at least it was when I went through their works in Berlin several years ago. Even were it of steel, I doubt if a magnet could be built powerful enough to attract or divert a Whitehead steel torpedo from its course unless it passed very close to the magnet, as any artificially erected magnetic force diminishes in strength very rapidly as the distance from the object is increased. Recall, for instance, the powerful magnets used in handling scrap and pig iron; while they will lift pigs or billets of iron weighing tons when in direct contact, they will not exert sufficient magnetic force to lift any iron at a distance of only a few inches.
Bombs.—The throwing of bombs in the water to intercept the oncoming torpedo might possibly divert its course if the torpedo were seen, but of all the ships that have been lost how few have seen the torpedo which did the damage! The white wake due to the air exhausted from the engines of the torpedo is frequently seen, but the air wake does not show on the surface from a torpedo running at any considerable depth until after the torpedo itself has passed on, as it takes quite some time for the air bubbles to reach the surface, and in a choppy sea the wake is very difficult to see in any case.
Discs.—Whirling discs spinning through the water to catch the nose of the torpedo and whirl it out of its course is one of the fanciful schemes which has attracted some press notice. The horsepower required to whirl the discs during one voyage would probably tax the full capacity of the ship to provide fuel and power enough to keep them whirling.
C-1, ONE OF THE LATER TYPE FRENCH SUBMARINES
French-Official Courtesy of Sea Power & Pictorial Press
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.