During World War I, the United States developed several types of body armor, including the chrome nickel steel Brewster Body Shield, which consisted of a breastplate and a headpiece and could withstand .303 British bullets at 2,700 ft/s (820 m/s), but was clumsy and heavy at 40 lb (18 kg). A scaled waistcoat of overlapping steel scales fixed to a leather lining was also designed; this armor weighed 11 lb (5.0 kg), fit close to the body, and was considered more comfortable.
French and German had this kind of armor too, but fun facts : soldiers often refused to use them, because of how uncomfortable and unwieldy they were. They were used by trench sentinels.
I guess they’d rather be dead than uncomfortable.