Technical Aspects of Fragmentation Bombs

In Vietnam the Americans are utilizing a new type of anti-personnel arm based on the following principle: a hollow metallic envelope into which are cast certain projectiles such as ball-bearing-like pellets, needles, etc., numbering into the hundreds. These explode on the ground or in the air to fire the projectiles in a sunburst pattern for many metres. The effects of the projectiles are insignificant on fixed installations. Two types of these weapons are principally in use in Vietnam. The ‘pineappleÂ' bomb with {117} cylindrically symmetrical explosion: this weapon consists of a hollow metallic envelope made of an alloy of copper and iron with traces of zinc, having a total weight of 800 grammes and a thickness of 7 millimetres. Into the envelope, which resembles the shape of a pineapple, are cast 300 pellets of steel 6.3 millimetres in diameter. On the top of the bomblet are placed six ‘wingsÂ' which are folded when the bomb is at rest and which snap up in flight by means of a spring at their base. These fins stabilize the fall of the bomb in the same manner as the feathers do a badminton shuttlecock. The lower part of the bomblet is closed with a metallic plate pierced by a hole through which penetrates the point of a spring-loaded firing pin. Upon impact - if the bomblet falls vertically, as it is supposed to - the spring releases and the percussive force causes the explosion of 160 grammes of Cyclotol A3 which is composed of 91 per cent hexogene trimethylene-trinitramine and 9 per cent wax, an explosive three times more powerful than TNT. The explosion projects the pellets in a sun-burst pattern at an angle of about 20° with the horizontal to a distance of 15 metres; the pieces of the casing are propelled about 50 metres. Craters from these bomblets are small: 30 to 40 centimetres maximum diameter in loose soil and with a depth of 10 to 20 centimetres; their damage to structures is insignificant.

Method of employment: a pod containing 19 cylindrical tubes of a diameter slightly larger than the bomblets is fixed beneath an aircraftÂ's wings and parallel to them. Each tube contains 20 bomblets with the fins folded back. The aeroplane flies horizontally at an altitude of about 800 metres and fires the pineapples from the tubes by means of a directed explosion of several grammes of powder. The bomblets disperse in the same manner as a ‘stickÂ' of parachutists over an elliptical zone about 500 metres long by 250 metres wide. This weapon was first used, to the best of our knowledge, on 8 February 1965 against Le Thuy, in the province of Quang Binh.

From a purely military point of view, these weapons had two drawbacks: 1. there were numerous ‘dudsÂ' as the bomblet did not always fall vertically as was necessary for proper detonation; 2. the horizontal, straight-and-level flight of the aircraft at the low level - no more than 1,000 metres - necessary to assure maximum effective dispersal of the pineapple bomblets rendered the attacking {118} aircraft extremely vulnerable to ground-fire. For these reasons the pineapple anti-personnel weapon seems to have been largely superseded by the ‘guavaÂ' bomb with spherically symmetrical explosion. This weapon is round, resembling a conventional hand grenade, and has a total weight of 400 grammes. Like the pineapple, it consists of a hollow envelope 7 millimetres thick of the same alloy and is filled with 50 grammes of Cyclotol A3. Into the casing are cast 260 to 300 steel balls 5.56 millimetres in diameter. Also cast into the casing in meridional direction are 4 small fins or ‘wingsÂ' which catch the wind and by friction set up a spinning motion along the polar axis. In the centre of the explosive filling a new type of detonator is located which operates by centrifugal force. This detonator consists of three small hammers which are cocked by the spinning of the bomblet and which are spring-loaded. If the spinning stops for any reason, the hammers fall, exploding the bomblet, and firing the steel pellets into an isotropic distribution in a sun-burst pattern for a distance of about 15 metres.

It is the nature of the bomb that when it touches the ground or even if, while in flight, it glances off a roof, a wall, or a branch of a tree, thereby interrupting or changing the axis of rotation away from the original polar axis, or, as shown by blast studies in Japan, if the axis changes spontaneously or the rate of spinning slows, the bomblet explodes. Like the pineapple, the craters produced are small and the effect of the bomblet on structures is insignificant. Method of employment: these bomblets are packed into a hollow #145;motherÂ' bomb casing about 2.1 metres long by 40 centimetres in diameter which holds roughly 640 guava bomblets. The mother bombs have a timing device which separates the container casing at an altitude of about 800 metres. The 640 guava bomblets are flung out and follow a parabolic trajectory and are distributed over the objective in an elliptical pattern about one kilometre long by about 500 metres wide.

This weapon was used for the first time on about 18 April 1966, on the village of Moc Chan in the Democratic Republic of Vietnam. Because of the spherical symmetry of the explosion and the tendency for a percentage of the bomblets to explode as air-bursts, traditional trenches and open individual shelters are rendered ineffective for cover; these weapons are therefore extremely {119} dangerous. They are usually employed in a three-stage raid: first comes observation, then bombardment with high explosives and/or napalm and then by CBUs (container bomb units) containing the guava steel pellet bombs.

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