So far we have said nothing about the seaplanes which were used in large numbers to watch for submarines. These were big flying boats in which speed was not a very important matter. One of the really big machines we developed, but which was not finished until after the war, was a giant with a 110-foot span and a body or hull 50 feet long. During the war seaplanes carried wireless telephone apparatus with which they could call to destroyers and submarine-chasers when they spotted a submarine. They also carried bombs which they could drop on U-boats, and even heavy guns with which they could fire shell. A still later development are the giant planes of the N. C. type with a wing-spread of 126 feet and driven by four Liberty motors. They carry a useful load of four and a half tons. [Illustration: (C) Underwood & Underwood The Flying-tank--an Armored German Airplane designed for firing on troops on the march] Early in the war, large guns were mounted on airplanes, but the shock of the recoil proved too much for the airplane to stand. However, an American inventor produced a gun which had no recoil. This he accomplished by using a double-end gun, which was fired from the middle. The bullet or shell was shot out at the forward end of the gun and a dummy charge of sand was shot out at the rear end. The sand spread out and did no damage at a short distance from the gun, but care had to be taken not to come too close. These non-recoil guns were made in different sizes, to fire 1-1/2-inch to 3-inch shell. THE AUTOMATIC SEAPLANE Another interesting development was the target airplane used for the training of aërial gunners. This was a small seaplane with a span of only 18-1/2 feet, driven by a 12-horse-power motor, the whole machine weighing but 175 pounds. This was sent up without a pilot and it would fly at the rate of forty to fifty miles per hour until its supply of gasolene gave out, when it would drop down into the sea. It afforded a real target for gunners in practice machines. [Illustration: (C) Underwood & Underwood An N-C (Navy-Curtiss) Seaplane of the type that made the first flight across the Atlantic] Early in the war an American inventor proposed that seaplanes be provided with torpedoes which they could launch at an enemy ship. The seaplane would swoop down out of the sky to within a short distance of the ship, drop its projectile, and fly off again, and the torpedo would continue on its course until it blew up the vessel. It was urged that a fleet of such seaplanes protected by a convoy of fast battle-planes could invade the enemy harbors and destroys its powerful fleet. It seemed like a rather wild idea, but the British actually built such torpedo-planes and tested them. However, the German fleet surrendered before it was necessary to blow it up in such fashion. AIRPLANES AFTER THE WAR