I have read several times that the reason General Pershing was so impressed by the DB was that he was riding in the back seat of a DB car when it ran over a land mine which exploded. It lifted the car about a couple of feet in the air, and severely dented the underside of the body but did not penetrate it. Pershing was convinced he would have been killed or injured in any other make of car.
John and Horace used chrome vanadium steel in the body as well as the running gear. It's so tough that it even makes repairs more difficult than with standard steel alloys.