The Submarine Torpedo Boat
Its Characteristics And Modern Development

i8o THE SUBMARINE TORPEDO BOAT ance of the water after the torpedo has left the tube, thus preventing the racing of the engine. In the early torpedoes, in fact until quite recently, steering in a horizontal plane was effected, or rather the torpedo was kept on a horizontal course, solely by the ac- tion of oppositely revolving propeller blades. This was effected by two propellers placed tandem at the tail, the after one being keyed to the engine shaft and the forward one being keyed to a loose sleeve fitted on the shaft and driven in an opposite direction by means of a set of bevel gearing. The necessity of having two propellers working in opposite directions arises from the thrust or tendency of a propeller to throw itself away from the direction in which it is revolving. Fixed vanes or guides were also provided at the stern. These were not however to steer the torpedo but rather to effect a steadiness, and tend to keep the torpedo on a straight course. In actual practice though it was found that no matter how carefully the torpedo had been tested and balanced it would behave in a very erratic manner when fired. Instances have been known when the torpedo would run a certain distance and then swerve to the right or left or perhaps dive to the bottom. In fact the writer has seen them perform a complete circle, coming back like a boom- erang and hitting the side of the ship from which they were fired. No practicable remedy was found for this objectionable feature until the advent of the gyroscope. Now by means of an ingenious device known as the Obry gear, acting in conjunction with rudders placed at the stern, the torpedo is steered in a horizontal plane just as is a ship. By the use of the Obry gear the torpedo can now be held true to