Where to armor the returning bombers

Question

In World War II, analysts studied bombers returning from missions and mapped where they were riddled with bullet holes: lots on the wings and fuselage, very few on the engines. The instinct is to reinforce the areas taking the most hits.

Where should you actually add the armor, and why?

Accepted Answer

Armor the engines, the places with the fewest holes. The data comes only from planes that returned. That is the trap: you are looking at a sample conditioned on survival. A plane hit in the wings or fuselage often limped home, which is exactly why you see so many holes there. A plane hit in the engines mostly did not come back, so those planes are missing from your sample entirely. The near-absence of engine holes among survivors is not evidence that engines rarely get hit; it is evidence that engine hits are fatal, and the planes that took them are lying at the bottom of the sea. This is Abr…

Where to armor the returning bombers

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