Every American WWII Helmet Was Secretly Two Helmets

Every American helmet of the Second World War was two helmets: a steel pot, and inside it a separate fibre shell on cotton straps. The usual explanation is comfort. It's wrong. When an M1 stopped a fragment, the steel caved inward and travelled with it — so the Army built the shell deliberately an inch too big and used the liner to hold a man's skull out of the way. This is the story of that inch, and what it cost.