Backfire

It has been estimated that during the First World War 75,000 French soldiers were killed or maimed by 'friendly fire', the euphemism commonly used for being killed by one's own colleagues or allies, presumably in error. As recently as the Gulf War the heaviest British casualties suffered in a single engagement were caused when US forces fired at British armoured vehicles, killing nine of the men inside. A quarter of all American casualties in 1991 were caused by other American soldiers How can this happen? How widespread is it? To what extent is the problem covered up?