Air burst
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An air burst occurs whenever an explosive device such as an anti-personnel artillery shell or a nuclear weapon is detonated in the air instead of on contact with the ground or target or a delayed armor piercing explosion. Aerial bursts may also arise from the explosion, above the ground, of incoming meteoroids as in the Tunguska event.
The principal military advantage of an air burst over a ground burst is that the energy from the explosion (as well as any shrapnel) is distributed more evenly over a wider area, however the peak energy is lower.
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[edit] History
Air burst artillery has a long history. The shrapnel shell, invented by Henry Shrapnel of the British army in about 1780, was widely used by the time of the War of 1812 and stayed in use until it was superseded during the First World War. The original shell was a hollow sphere filled with musket balls and a charge of gun powder. A burning fuse caused the charge to explode, bursting the shell and spraying the enemy with lead musket balls. The shell was subsequently improved and made in the cylindrical, pointed shape of normal artillery shells. Mechanical and chemical time fuses caused the detonation of the powder charge which launched the musket balls out the front of the cylindrical shell. Shrapnel shells have had various names including spherical case shot, the original name. The name shrapnel was a nickname given to the shell to honour the inventor. The common use of the term "shrapnel" to describe modern artillery shells is technically not correct. Modern shells produce fragments and splinters, not shrapnel.
When infantry moved into deep trenches, shrapnel shells were rendered useless and high explosive shells were used to attack field fortifications and troops in the open. The time fuses for the shells could be set to function on contact or in the air. During the Second World War, a Variable Time Fuse was developed. This fuse could not be set by the gun detachment but was controlled by a doppler radar device which cause the shell to explode when near the target. Sixty feet above the ground was standard. Air bursts were used in the first World War to shower enemy positions and men with shrapnel to kill the largest possible number of them with a single burst, assuming that the blast was directly over the trench the men were positioned in.
During the Vietnam War, air bursting shells were used to great effect to defend US Army bases. This tactic was known as 'Killer Junior' when referring to 105 mm or 155 mm shells, and 'Killer Senior' when employed with larger howitzers.
Some anti-personnel land mines such as the "Bouncing Betty" fire a grenade into the air which detonates somewhere between five and half and six feet, causing the shrapnel to fly out at head or chest level, severely maiming anyone within a fifteen foot radius.
With nuclear weapons, the air burst—usually several hundred to a few thousand feet in the air—allows the shockwave of the fission or fusion driven explosion to destroy the largest possible number of buildings, military units or vehicles, etc. This also minimizes the generation of irradiated soil and other debris (fallout) by keeping the fireball from touching the ground, limiting the amount of additional debris that is vaporized and drawn up in the radioactive debris cloud.
[edit] Tactics
Air bursts are used primarily against infantry in the open or unarmored targets, as the resulting shrapnel covers a large area but will not penetrate armor, entrenchments, or fortifications. U.S. Army tactics call for the use of air-bursting munitions at three levels: first by MLRS bomblets against exposed command and logistics units in the enemy's rear, second by 155 mm artillery shells against infantry positions, and third by mortars in order to provide cover for advancing units.
