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.
Courtesy of "Scientific American"
An Italian "Sea-tank" climbing over a Harbor Boom
(C) Underwood & Underwood
Deck of a British Aircraft Mothership or "Hush ship"
THE AWKWARD "EAGLES"
A curious boat that we undertook to furnish during the war was a cross between a destroyer and a submarine-chaser. After the submarine had been driven out to sea its greatest foe was undoubtedly the destroyer, and frantic efforts were made to turn out as many destroyers as possible. But it takes time to build destroyers and so a new type of boat was designed, to be turned out quickly in large numbers. A hundred and ten "Eagles" (as these boats are called) were ordered, but the armistice was signed before any of them were put into service; and it is just as well that such was the case, for in their construction everything was sacrificed to speed of production. As a consequence they are very ugly boats, with none of the fine lines of a destroyer, and they roll badly, even when the sea is comparatively peaceful. They are five-hundred-ton boats designed to make eighteen knots, which would not have been fast enough to cope with U-boats, because the latter could make as high a speed as that themselves, when traveling on the surface, and the two 4-inch guns of the Eagles would have been far outranged by the 5.9-inch guns of the larger U-boats.