Bombs

The AAF chooses bomb designs for specific types of offensive missions as carefully as the aircraft engineer designs his plane.

BOMBS of the Army Air Forces are pounding out the shape of victory. Air offense has proved to be the most effective power unleashed in World War II.

From the beginning, the AAF has understood the aerial bomb as an offensive weapon. The Ordnance Department, with the Air Forces, has developed, tested and proved every type of bomb, studied the suitability of each to a given mission, observed their power and effectiveness, and generally kept pace by fitting bomb designs to the bombing potentials of plane types as they evolve. Today we are delivering those bombs — the most efficient in the world — straight to the enemy. What is a bomb?

Ordnance Department defines it as a missile intended to be dropped from aircraft. Five kinds of bombs are used by the Army Air Forces today:

  1. demolition,
  2. fragmentation,
  3. chemical,
  4. practice, and
  5. drill and gauge.
Of these, the first three types are the only ones used in combat.

Should the target be such that it is necessary to expend a tremendous amount of energy within it or against it — that is, to blast walls apart, to burst a hole in a ship, to excavate the foundations of some structure, or to crumple a dam — then demolition bombs are used.

A demolition bomb is really a balanced, streamlined package carrying a charge of high explosive to the point where it can be used best. It is housed in a bomb body, or case, which is made light and yet strong. The bomb must remain in one piece until it detonates, generally within the target, instead of breaking open on first impact. In order to obtain the penetration necessary for different targets and still carry the maximum amount of explosive, demolition bombs are made from several different metals of varying hardness and varying case thickness. They are divided into the following types:

The GP bomb is made of such strength that it can be dropped without rupturing against a concrete slab four feet thick from an altitude of 8,000 feet. Using a delay-action fuse, bombs of this type would crash through to the basement of most buildings, bury themselves several feet in the ground near a bridge or penetrate the deck of any seacraft except cruisers and battleships.

The GP bomb is made in five sizes:

  1. The 100-pound bomb can demolish a two-story building, wreck a locomotive, gun installation, or other machinery from 10 feet, damage an airplane from 75 feet.
  2. The 250-pounder will destroy walls and floors of all buildings except skyscrapers, will sink or severely damage all seacraft — except battleships and cruisers — as far as 20 feet away, tear up railway tracks for a distance of 30 feet.
  3. The 500-pound bomb will cause 75 feet of concrete dock to collapse from 25 feet away, will wreck steel railway bridges and subway passages, sink or seriously damage light cruisers as far away as 25 feet, and demolish most tanks.
  4. The 1,000-pound bomb can displace the piers and spans of the heaviest bridges.
  5. 5. The 2,000-pound (one ton) bomb will crack or burst a large hole in dams, sink or seriously damage modern battle cruisers and battleships when direct hits, or as far as 35 feet away when exploded in the water.

The Laboratory of Wartime Operations has produced a mathematical formula on the underwater effect of GP demolition bombs.

Pressures of four tons per square inch are required for hull rupture of surface vessels of the most modern construction. That is, there is a danger area around and under a vessel, depending upon the size of the bomb, where hull rupture and consequent sinking will occur.

There is a larger area in ratio of magnitude of about 1 to 80 of shock limit that will have little effect on outboard fittings. Persons within that water area, however, will be killed or seriously injured by the shock of the blast.

Truly a general purpose bomb, the GP can be used most effectively against nearly every type of military objective by using the proper tactics. It can be used by the AAF, the US Navy and the RAF. It can even split the sides of a submarine on detonating at the proper depth. This is accomplished by using a delayed-action fuse or the Navy's hydrostatic fuse.

To blast the vital organs of targets which the GP will not penetrate, semi-armor piercing bombs were developed. They are made in sizes of 500 and 1,000 pounds. The heaviest tank can be punctured by the 500-pound semi-armor piercing bomb while the 1,000-pounder will penetrate the side or deck of all naval craft except battle cruisers and battleships.

Seacoast mortar shells have been converted and adapted with fins as armor-piercing bombs. These bombs are generally capable of penetrating the armor of battle cruisers and battleships, and a direct hit exploding within the ship will cause serious damage. This type is not generally used since the explosive content is so small that a near miss will have negligible effect.

On the other hand, a 2,000-pound GP bomb will do considerable damage as far as 55 feet from a battleship. The various weights of AP bombs are 699, 800, 900, 1,000, 1,400 and 1,600 pounds.

Tamping produces the maximum destruction in an explosive. The destruction caused by a well-tamped explosive may be 4.5 times as great as the same amount untamped. To the bomb expert this means the explosive must be confined within the target. There must be no holes through which its energy may escape. To accomplish this the bomb is made to penetrate a building, the ground, a ship, or the water beside the ship.

With the light-case bomb, no penetration can be obtained. The case will rupture and spill the explosive on impact with practically all objects except water. Then why use it at a11? The light-case bomb was designed for a target that provides its own tamping — a congested city block. The "block-buster" has 3,362 pounds of explosive cast into a bomb weighing 4,200 pounds and equipped with an instantaneous fuse so that the terrific blast will occur before the bomb case ruptures. Our planes patrolling the seas surprise the enemies' submarines continually. To knock out the U-boat, the maximum blast must be delivered to the proper depth. This is accomplished by one of two depth bombs, the 325-pound Mark 17 and the 650-pound Mark 29. These bombs are of very light case, having about 75 per cent explosive filler and a Navy hydrostatic fuse. The operation of the fuse depends upon the pressure upon it and consequently its depth below the surface. The depth may be pre-set.

A second kind of AAF bomb is the fragmentation type used against ground forces and light material — trucks, airplanes and encampments. Its destructive power results wholly from fragmentation of the bomb case. Fragmentation bombs have been so designed that they break into 1,000 to 1,500 pieces weighing about .3 ounce, with velocities up to 4,000 feet per second. At 200 feet, the fragments will go through a wing or gas tank, cut through tires and control wires, perforate radiators and intercoolers. Ground crews need 25 to 30 hours to repair planes damaged by fragments of bombs placed 90 feet or less from the plane.

There are two kinds of fragmentation bombs. One is anti-personnel, designed to burst on contact with the ground and spray missiles the size and speed of a .30 caliber rifle bullet. One design has fins for high-altitude release, either singly or in clusters. By using a mechanical time fuse in a fragmentation bomb of the fin type, this bomb can be dropped on a lower flying formation of airplanes and made to explode in their midst. This is the antiaircraft fragmentation bomb.

Realists always, air ordnance experts have not neglected chemical bombs and the enemy knows that they will be used, if necessary, in retaliation for gas attacks. Some samples:

  1. Gases of the type called harassing agents hinder operations of troops by forcing them to wear gas masks or to remove them in order to sneeze or vomit, thus rendering them vulnerable to more potent gases.
  2. Casualty agents, such as chlorine, mustard gas and phosgene, do bodily harm.
  3. Screening smokes produce dense obscuring smoke in the air.
  4. Incendiary agents produce a tremendous amount of heat, set fire to combustible material.

The chemical bomb case is light steel, may be filled with almost any chemical agent, weighs about 100 pounds.

Filled with mustard gas, it becomes a casualty bomb. A filling of white phosphorous makes it an incendiary or smoke bomb.

A plane may carry 1,500 to 2,000 small incendiary bombs. These weigh about four pounds, burn at temperatures of 3,300° to 4,500°, can start fires in cities, airdromes or encampments.

Hand in hand with combat operational bombs, the AAF at war uses vast quantities of practice bombs. These are the key to marksmanship. Training with the 100-pounders is only a step from laying the real "eggs." The AAF has not been content to develop bombs. Our airmen have learned to use them with devastating effect.

Latest technique is minimum altitude, or skip, bombing which proved so effective in the Battle of the Bismarck Sea. By this method the planes attack at maximum speed from an altitude just high enough to clear surface obstructions. The bombs are dropped with such extreme accuracy, even against moving targets, that no tank or armored vehicle is safe. New sights had to be developed, new fuses made.

Another special tactical method is high-altitude night bombing. Flares dropped to illuminate the target descend to a certain predetermined altitude. Here a special fuse causes a parachute to open, allowing slow descent of the flare. Then the fuse ignites the flare, which burns with a brilliancy of 800,000 or more candlepower.

Every mission requires its own bombs and fuses, its own tactics for a custom-built attack on the target. This is a game as grim as death and it has three fundamental rules:

  1. Always use a bomb of sufficient size to accomplish the destruction desired. If a 1,000-pound bomb is required, a 600- pound bomb will not suffice — and a two-ton monster is wasteful.
  2. Having determined the proper size of bomb, never use a heavier bomb, but carry more of the right weight bombs and thus increase the probability of securing the necessary hits.
  3. Select the fuse that will give the maximum effect against the given target.

These "tactics of realism" explain American bombing triumphs in every theater.

We have the world's best bombers, the best crews, the best bombs. In all of these — together and not singly — we have tools to win the war.

This article was originally published in the October, 1943, Special Issue US Air Forces At War issue of Flying magazine, vol 33, no 4, pp 111-113, 268.
The PDF of this article includes photos of a 4,000-lb bomb, a stick of fragmentation bombs being dropped, bombing up the wing racks of a B-25, bombing up a B-25 bomb bay, mounting an oversize bomb under a B-26.
Photos credited to Army Air Forces.