22 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
Ime. The torpedo leaves the tube with a moderately low velocity, 
and is then driven forward through the water by its own propellers, 
operated by compressed air as previously described. The explosive 
charge carried in the head is fired by percussion when the torpedo 
strikes. The depth at which the torpedo will travel is reeulated by 
the operation of a plunger, which is-acted on by the water pressure 
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anes as 
Fia. 8.—Defensive mine system. Entrance to harbor. 
and controls a steering device which operates a horizontal rudder 
attached to the rear of the torpedo (fig. 9.) 
DIRECTING MECHANISM. 
The torpedo is guided in direction through the operation of a 
rapidly rotatmg gyroscope or small wheel which controls a steering 
engine. This gyroscope is usually of a turbine construction and is 
rotated by compressed air at a very high rate of speed. In accord- 
ance with a well-known principle of mechanics, such a rapidly rotat- 
