A "friendly fire incident" refers to a military situation where forces or material assets of one side are attacked and damaged in error by those of their own or their allies. In British military parlance these incidents are referred to as blue-on-blue. The term "blue-on-blue" originates from wargaming exercises where friendly forces are blue and enemy forces are red. The term fratricide (killing one's brother) is also sometimes used but more properly refers to incident of deliberate attacks on one's own forces.
Rightly or wrongly, the armed forces of the US are widely believed to be more prone to friendly fire incidents than the military of other nations. The Pentagon estimates at US friendly fire deaths are:
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