When inventor Guy Otis Brewster offered his Brewster Body Shield to the soldiers of World War I, he demonstrated its efficacy by standing before a Lewis machine gun firing bullets at full velocity, about 2,700 feet per second.

All that energy heated the breastplate, but Brewster said he felt “only about one tenth the shock which he experienced when struck by a sledge-hammer.”

Unfortunately the armor weighed 40 pounds, which made it cumbersome in the field.

(Bashford Dean, Helmets and Body Armor in Modern Warfare, 1920.)