Why Armor Was Added to Fighters Where Bullet Holes Were Not Found

During World War II, fighter planes would come back from battle with bullet holes. The Allies initially sought to strengthen the most commonly damaged parts of the planes to increase combat survivability. A mathematician, Abraham Wald, pointed out that perhaps the reason certain areas of the planes weren't covered in bullet holes was that planes that were shot in certain critical areas did not return. This insight led to the armor being re-enforced on the...