The war brought forth many new types of projectiles: shells loaded with lethal gases; shells which left a trail of smoke whereby their course could be followed when fired at aircraft; shells that illuminated the battlefield at night, etc. The searchlight shells carried a number of “candles,” each furnished with a little parachute so that when the shell exploded the burning candles would settle slowly to the ground, all the while casting a brilliant light on operations below.
AERIAL BOMBS
Obviously, hurling projectiles from the air is a much simpler matter than projecting them from the ground. No propellant is required to carry them to the target and no rifling is necessary to keep them head-on in the direction of flight. They are pulled instead of being pushed and can easily be kept in their course by means of rudder planes. But hitting a target from an aeroplane is like hitting a swiftly moving object from the ground. The target is seemingly flying past the aeroplane and in calculating where the aerial bomb will strike the speed of the plane through the air and its height above the ground must all be taken into consideration.
Naval warfare is a fight of fort against fort and consequently the high explosive projectile is the principal one used. The shells must be able to penetrate heavy steel armor and explode within the hull of the vessel. In addition to these we have the torpedoes fired by destroyers and submarines which explode an enormous quantity of high explosive against the hull of the vessel. No attempt is made to penetrate the skin of the vessel, but the explosive, tamped by a considerable depth of water, delivers a very heavy crushing blow against the side of the hull.
AUTOMATIC CONTROL OF SUBMARINE TORPEDOES
It is wrong to speak of firing a torpedo. A torpedo is really an automatic, self-propelled, submarine boat. All that the destroyer or submarine does is to set the steering gear in this little boat and then launch it at the enemy with a blast of air that ejects it from the torpedo tube. Most of the body of the torpedo is filled with compressed air which drives a small air motor coupled to a pair of propellers. These propellers run in opposite directions so as to balance each other and they drive the torpedo through the water at a speed of about forty miles per hour. The speed falls off gradually as the air supply is exhausted.
To hold the torpedo on its course horizontal and vertical rudders are employed. The vertical rudder is controlled by a gyroscope which turns it this way or that according as the torpedo tends to veer off its course.
The value of a torpedo lies in its concealment. Were it to travel on the surface the vessel against which it was directed might be able to avoid it; furthermore the action of the waves would tend to disturb the gyroscopic steering mechanism and the torpedo would pursue an erratic course. For this reason it must travel under water at a depth sufficient to avoid surface disturbances. There is also a distinct advantage in having a good cover of water over the torpedo when it strikes its target because the force of the explosion, although felt in all directions, is mainly expended along the line of the least resistance. If the depth of water over the torpedo is slight, most of the force will be expended upward and only a comparatively small part will act against the hull of the vessel. It was the practice of the Germans to set their torpedoes for a depth of about ten feet.
To hold a torpedo at a fixed depth a very delicate hydrostatic valve is employed which operates the diving rudders. The valve is set for a certain depth or weight of water. If the torpedo goes below this depth, the weight of the water bearing on this valve presses it down and thereby tilts the diving rudders until the torpedo comes back to the required depth. If it rises above the depth for which it is set, the valve feels the reduction of water pressure and tilts the rudders in the opposite direction to correct the deviation from the predetermined line of travel. Once the valve has been set the torpedo takes care of itself automatically. It may be discharged from any depth or be dropped from torpedo tubes on the deck of a ship and after a few undulations it will find its depth and hold it as long as it keeps running.