blue on blueˌblue on ˈblue adjective 
used to describe an occasion during a battle or a war when a soldier, sailor, or pilot is accidentally killed by their own army: 
a ‘Blue on Blue’ incident which saw an RAF jet brought down by a Patriot missile
used to describe an occasion during a battle or a war when a soldier, sailor, or pilot is accidentally killed by their own army: a ‘Blue on Blue’ incident which saw an RAF jet brought down by a Patriot missile