How have courts considered whether the discharge of a missile by the enemy was a cause of injury?

Helper J.A. refers to an English case at p. 19, paras. 97 and 98, as follows: An English case is particularly helpful. In Minister of Pensions v. Chennell, [1947] 1 K.B. 250, a bomb dropped by enemy aircraft was found unexploded by a boy and was taken home. The boy subsequently took the bomb to a public thoroughfare. He tampered with it with the result that it exploded causing injury to a girl. The issue before the court was whether the girl’s injury was a war injury under the Personal Injuries (Emergency Provisions) Act, 1939. Denning, J. as he then was, considered whether the injury was “caused by” the discharge of the bomb by the enemy (as required by the provisions of the Act). He began at p. 252: “Much depends on the right approach. The best way is to start with the injury and inquire what are the causes of it. Sometimes there may be a single cause. More often there is a combination of causes. If the discharge of a missile or other event may be properly said to be a cause of the injury, that is sufficient to entitle the claimant to an award of a pension, notwithstanding that there may be other causes co-operating to produce it, whether they be antecedent, concurrent or intervening. It is not necessary that the discharge of the missile or other event should be 'the' cause of the injury in the sense either of the sole cause or of the effective and predominant cause.” He concluded at p. 257: “… applying the principles that I have stated, I am of the opinion that in this case the dropping of the bomb by the enemy was a cause of the injury and that the boy’s interference was not so powerful an intervening cause as to supersede it. The injury was therefore ‘caused by’ the dropping of the bomb by the enemy.” (underlining mine)