friendly fire

It is clear that the firing of very heavy guns, or the enemy's fire in return, would very seriously interfere with an abbatis, or anything of that kind, and it will be only something of the lightest character, or something that is placed at a considerable distance from the friendly fire, the fire of the gun itself, that would remain.

1867 June 3, A[lexander] Moncrieff, quoting Jasper Selwyn, “[Evening Meeting.] Further Particulars Regarding [Colin Scott-]Moncrieff's Protected Barbette System.”, in Journal of the Royal United Service Institution, Whitehall Yard, volume XI, number XLIV, London: […] W[illiam] Mitchell and Co., […], published 1868, →OCLC, page 256

The slaughter of one's own troops by being fired into by their friends in rear. We are very much concerned over the question of avoiding loss from the enemy's bullets while passing through the danger zone, but what have we done to avoid our bravest fellows, the survival of the fittest, those who have gotten to the front and have held on to hard-won positions—what have we done to avoid their being shot to pieces by friendly fire? Absolutely nothing that we have ever heard of—and yet this is one of the most serious problems that confronts the leader of troops. Courage before the enemy will quail before a fire from the rear.

1910 May–June, P. E. T., “[Reviews and Exchanges.] The Franco-German War.”, in T[heophilus] F[rancis] Rodenbough, editor, Journal of the Military Service Institution of the United States, volume XLVI, number CLXV, New York, N.Y.: Military Service Institution, →OCLC, page 552