The bomb-thrower reads the altitude of his airship as indicated by his barometer or other recording instrument, and by means of a table at his command ascertains in a moment the time which will elapse before the bomb strikes the ground. The automatic detonator is set in motion and the bomb released to explode approximately at the height to which it is set. When it bursts the full force of the explosion is distributed downwards and laterally. Owing to the difficulty of ensuring the explosion of the bomb at the exact height desired, it is also made to explode upon impact so as to make doubly sure of its efficacy.
Firing timed bombs from aloft, however, is not free from excitement and danger, as the experience of a French airman demonstrates. His dirigible had been commanded to make a night-raid upon a railway station which was a strategical junction for the movement of the enemy's troops. Although the hostile searchlights were active, the airship contrived to slip between the spokes of light without being observed. By descending to a comparatively low altitude the pilot was able to pick up the objective.
Three projectiles were discharged in rapid succession and then the searchlights, being concentrated, struck the airship, revealing its presence to the troops below. Instantly a spirited fusillade broke out. The airmen, by throwing ballast and other portable articles overboard pell-mell, rose rapidly, pursued by the hostile shells.
In the upward travel the bomb-thrower decided to have a parting shot. The airship was steadied momentarily to enable the range to be taken, the automatic detonator was set going and the bomb slipped into the launching tube. But for some reason or other the missile jambed.
The situation was desperate. In a few seconds the bomb would burst and shatter the airship. The bomb-thrower grabbed a tool and climbing into the rigging below hacked away at the bomb-throwing tube until the whole equipment was cut adrift and fell clear of the vessel. Almost instantly there was a terrific explosion in mid-air. The blast of air caused the vessel to roll and pitch in a disconcerting manner, but as the airman permitted the craft to continue its upward course unchecked, she soon steadied herself and was brought under control once more.
The bomb carried by aeroplanes differs consider ably from that used by dirigibles, is smaller and more convenient to handle, though considering its weight and size it is remarkably destructive. In this instance complete reliance is placed upon detonation by impact. The latest types of British war-plane bombs have been made particularly formidable, those employed in the "raids in force" ranging up to 95 pounds in weight.
The type of bomb which has proved to be the most successful is pear-shaped. The tail spindle is given an arrow-head shape, the vanes being utilised to steady the downward flight of the missile. In falling the bomb spins round, the rotating speed increasing as the projectile gathers velocity. The vanes act as a guide, keeping the projectile in as vertical a plane as possible, and ensuring that the rounded head shall strike the ground. The earlier types of bombs were not fitted with these vanes, the result being that sometimes they turned over and over as they fell through the air, while more often than not they failed to explode upon striking the ground.
The method of launching the bomb also varies considerably, experience not having indicated the most efficient method of consummating this end. In some cases the bombs are carried in a cradle placed beneath the aeroplane and launched merely by tilting them in a kind of sling, one by one, to enable them to drop to the ground, this action being controlled by means of a lever. In another instance they are dropped over the side of the car by the pilot, the tail of the bomb being fitted with a swivel and ring to facilitate the operation. Some of the French aviators favour a still simpler method. The bomb is attached to a thread and lowered over the side. At the critical moment it is released simply by severing the thread. Such aeroplane bombs, however, constitute a menace to the machine and to the pilot.
Should the bomb be struck by hostile rifle or shell fire while the machine is aloft, an explosion is probable; while should the aero plane make an abrupt descent the missiles are likely to be detonated.
A bomb which circumvents this menace and which in fact will explode only when it strikes the ground is that devised by Mr.
Marten-Hale. This projectile follows the usual pear-shape, and has a rotating tail to preserve direction when in flight. The detonator is held away from the main charge by a collar and ball-bearing which are held in place by the projecting end of a screw-releasing spindle. When the bomb is dropped the rotating tail causes the spindle to screw upwards until the projection moves away from the steel balls, thereby allowing them to fall inward when the collar and the detonator are released. In order to bring about this action the bomb must have a fall of at least 200 feet.
When the bomb strikes the ground the detonator falls down on the charge, fires the latter, and thus brings about the bursting of the bomb. The projectile is of the shrapnel type. It weighs 20pounds complete, is charged with some four pounds of T.N.T., and carries 340 steel balls, which represent a weight of 5 3/4pounds.
The firing mechanism is extremely sensitive and the bomb will burst upon impact with the hull of an airship, water, or soft soil. This projectile, when discharged, speedily assumes the vertical position, so that there is every probability that it will strike the ground fairly and squarely, although at the same time such an impact is not imperative, because it will explode even if the angle of incidence be only 5 degrees. It is remarkably steady in its flight, the balancing and the design of the tail frustrating completely any tendency to wobble or to turn turtle while falling.
