Flechettes are an anti-personnel weapon that is generally fired from tanks. The shell explodes in the air and releases thousands of metal darts 3.75 mm in length, which disperse in a conical arch three hundred meters long and about ninety meters wide. .
The IDF uses flechette shells that are 105 mm in diameter and are fired from tanks.
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The IDF used flechettes in Lebanon against the Hizbullah and the other militias fighting against Israel. The flechettes killed and wounded dozens of Lebanese civilians, who were not involved in the hostilities, including children.
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These claims cannot justify the use of flechette shells by the IDF in the Gaza Strip.While flechettes are not expressly forbidden in international humanitarian law under all circumstances, but other rules of humanitarian law render their use in the Gaza Strip illegal. One of the most fundamental principles is the obligation to distinguish between those involved in the hostilities and those who are not involved in the fighting, and to avoid to the extent possible injury to those who are not involved in combat. Deriving from this principle, is the prohibition on the use of an imprecise weapon which is likely to result in civilian injuries.
The long killing range of the shell makes its use in populated areas, such as the Gaza Strip, a type of indiscriminate firing, in which there is a particularly high danger of innocent civilians being harmed. In addition, during combat in a built-up area, the likelihood of errors in identifying the source of light-weapons fire is particularly great. Because of the duty to limit to the extent possible the damage to innocent civilians, added caution is required when selecting the military response, including the type of ammunition.
http://www.btselem.org/English/Open_Fire_Regulations/Flechette.asp