British soldier with experimental body armor meeting with his medieval counterpart; ca. October 1917
Before the First World War, no military used true protective helmets; Pith helmets and Pickelhaubes technically are helmets, but offer very little protection against bullet fragments and shell splinters. Similarly, any armor used previously to the First World War would be of medieval-inspired designs, for instance in the armor found on heavy cavalry. Even the French helmet from that conflict was designed with medieval aesthetics in mind.
In the First World War context, modern body armor would have primarily been used for machine gunners and others in static positions exposed to heavy small arms fire. This, though, is the most modern in appearance and design that I’ve seen – the groin protector is surprisingly sophisticated.
The First World War was the true introduction of so much modern military equipment on a vast scale: helmets and body armor designed for modern threats, gas masks, tanks, fighter and bomber aircraft, light machine guns, submachine guns, semi-automatic battle rifles, and more. The Second World War, with the exception of the nuclear bomb, offered more incremental improvements than revolutionary ones.