The war on the submarine was fought mainly from the surface of the sea and from the air above the sea, and naturally it resulted in many interesting naval developments.
As described in Chapter XIII, the first offensive measure against the U-boat was the building of swarms of speedy motor-boats which drove the invaders away from harbors and into the open sea. To follow the U-boats out into rough water larger submarine-chasers were built, but even they could not cope with the enemy far from the harbors.
The Italians made excellent use of speedy motor-boats in the protected waters of the Adriatic Sea. One type of motor-boat was equipped with two torpedo-tubes in the bow. Small 14-inch torpedoes were used, but as each torpedo carried two hundred pounds of high explosive, the motor-boat was a formidable vessel if it crept in close enough to discharge one of these missiles at its foe.
On one occasion, a patrol of these little boats sighted a couple of Austrian dreadnoughts headed down the coast, surrounded by a screen of ten destroyers. Favored by the mist, two of the motor-boats crept through the screen of destroyers, and torpedoed the battle-ships. Then they made good their escape. A destroyer that pursued one of the boats decided that the game was not worth while when it was suddenly shaken up by the explosion of a depth bomb dropped from the motor-boat.
The Italians showed a great deal of naval initiative. They were forever trying to trap the Austrian fleet or to invade its harbors. Like all other naval powers, the Austrians protected their harbors with nets and mines. It was impossible for submarines to make an entrance and the ports were too well fortified to permit an open attack on the surface. Nevertheless, the Italians did break through the harbor defenses on one or two occasions and sank Austrian war-vessels. Again it was with a small boat that they did the trick.
The nets which the Austrians stretched across their harbor entrance were supported on wooden booms or logs which served as floats. These booms offered an effective bar to small boats which might attempt to enter the harbor under cover of darkness. But the Italians found a way to overcome this obstruction. They built a flat-bottomed motor-boat which drew very little water. Running under the boat were two endless chains, like the treads of a tank. In fact, the boat came to be known as a "sea tank." The chains were motor-driven and had spiked sprockets, so that when a boom was encountered they would bite into the wood and pull the boat up over the log, or maybe they would drag the log down under the boat. At any rate, with this arrangement it was not very difficult to pass the boom and enter the harbor. At the rear the chains were carried back far enough to prevent the propeller from striking when the boat had passed over the log.