The Submarine Torpedo Boat
Its Characteristics And Modern Development

DESIGN OF THE SUBMARINE TORPEDO BOAT 93 four lengths of the boat. This is a quality wofully lack- ing in submarines at the present time. The only method of accomplishing this has been by placing the propellers at the forward end of the boat. By this means it has been found possible to turn the boat about in less than three lengths. Submerged it is the only possible way of steering the vessel in a horizontal plane without broaching or performing the evolutions of a spiral. Under water navigation is carried on by the aid of the gyroscopic compass and the periscopes. Two periscopes are now always required in order that there may be two lookouts when submerged and when running awash a third lookout in the conning tower. The advantage of this is at once apparent. The eyepieces or image reflecting ends of both periscopes are within the hull in the central operat- ing compartment. They must be so installed that no injurious vibrations are produced when traveling full speed submerged. Formerly they were constructed so as to be drawn down into the hull for a considerable por- tion of their length when submerged but this was of no advantage for their purpose is to allow the hull of the boat to remain submerged as deep as possible while the object glass of the periscope is above the surface; the method has now been abandoned. The first periscope about which there is anything known was invented in France in 1854 by Marie Davy, but it was about fifty years before they began to take any prac- tical shape. The earlier periscopes were frail and leaky, and became cloudy with moisture of condensation within a short while, making them useless. The image became inverted when looking to the rear, and they were alto-