I recommend this very interesting old book about WWI-era helmets, shields and body armour.
I am in awe of the researching skills that authors needed in the pre-internet age. This author certainly had huge travel expenses for this book.
Especially interesting to me were the good reviews for the "jazeran" body armour (p. 255ff):
related Defence and Freedom text:
The jazerans illustrated herewith furnished a remarkably comfortable body defense; they were worn hours at a time and under difficult conditions by various experimenters. The reports declare that they did not cause great discomfort, even though their weight was considerable (eleven pounds). The scales of plates of which they were made up were pressed in manganese steel of helmet thickness and were then riveted to a leather lining; they withstood the test of service ammunition with revolver. These defenses of both types were sent abroad and tested at American Headquarters. The report upon them stated that they have "excellent qualities" and were "recommended as a body armour, thoroughly practicable, no inconvenience to wearer, comfortable, silent."
Another shot at the historical failure of fragmentation protection vest procurement