It is also fitted with a safety fork and an inlet valve cover. Upon launching, the safety fork is knocked off, and the valve cover is removed to allow water to enter. When the depth charge gets about 12 to 15 feet below the surface, the water pressure is sufficient to extend a bellows in the booster extender. Notice that the detonator fits into a pocket in the booster. Unless the detonator is in this pocket, it cannot set off the booster charge.
Nothing further happens until the detonator fires.
As you can see, the detonator fits into the end of the pistol, with the firing pin aimed at the detonator base. The pistol also contains a bellows into which the water rushes as the charge goes down. As the pressure increases, the bellows begins to expand against the depth spring. You can adjust this spring so that the bellows will have to exert a predetermined force to compress it. Since the pressure on the bellows depends directly on the depth, you can select any depth on the dial at which you wish the charge to go off.