Figure  10-2.-Depth-setting  dial. into the detonator. The booster, already in position, then fires and, in turn, sets off the entire load of TNT. These  two  bellows—operated  by  hydrostatic pressure—serve two purposes. First, they permit the depth  charge  to  fire  at  the  proper  depth;  second,  they make the charge safe to handle and carry. If you should accidentally  knock  the  safety  fork  and  the  valve  inlet cover off on deck, nothing would happen. Even if the detonator should go off while you were handling the charge, the main charge would not fire unless the booster was  in  the  extended  position. Guiding  Torpedoes To keep a torpedo on course toward its target is a job.  Maintaining  the  proper  compass  course  with  a gyroscope is only part of the problem. The torpedo must travel at the proper depth so that it will neither pass under the target ship nor hop out of the water on the way. As  figure  10-3  shows,  the  torpedo  contains  an air-filled chamber sealed with a thin, flexible metal plate, or diaphragm. This diaphragm can bend upward or downward against the spring. You determine the spring  tension  by  setting  the  depth-adjusting  knob. Suppose  the  torpedo  starts  to  dive  below  the selected depth. The water, which enters the torpedo and surrounds the chamber, exerts an increased pressure on the diaphragm and causes it to bend down. If you follow the lever system, you push forward. Notice can see that the pendulum will that a valve rod connects the Figure 10-3.-Inside a torpedo. pendulum to the piston of the depth engine. As the piston moves to the left, low-pressure air from the torpedo’s air supply enters the depth engine to the right of the piston and pushes it to the left. You must use a depth engine because the diaphragm is not strong enough to move the rudders. The  piston  of  the  depth  engine  connects  to  the horizontal  rudders  as  shown.  When  the  piston  moves  to the left, the rudder turns upward and the torpedo begins to rise to the proper depth. If the nose goes up, the pendulum  swings  backward  and  keeps  the  rudder  from elevating the torpedo too rapidly. As long as the torpedo runs at the selected depth, the pressure on the chamber remains constant and the rudders do not change from their  horizontal  position. Diving Navy  divers  have  a  practical,  first-hand  knowledge of hydrostatic pressure. Think what happens to divers who go down 100 feet to work on a salvage job. The pressure on them at that depth is 8,524 pounds per square foot! Something must be done about that, or they would be flatter than a pancake. To  counterbalance  this  external  pressure,  a  diver wears a rubber suit. A shipboard compressor then pumps pressurized  air  into  the  suit,  which  inflates  it  and provides oxygen to the diver’s body as well. The oxygen enters  the  diver’s  lungs  and  bloodstream,  which  carries it to every part of the body. In that way the diver’s internal pressure is equal to the hydrostatic pressure. As the diver goes deeper, the air pressure increases to meet that of the water. In coming up, the pressure on the air is gradually reduced. If brought up too rapidly, the diver gets the “bends.” That is, the air that was dissolved in the blood begins to come out of solution 10-3