before the US entered the first world war, our experience in the Phillipenes with the Moro tribes had already convinced some that soft caps were not ideal headwear for combat. The Brits trench experiences  in 1915 underscored that modern wars demanded better headgear to stop "wastage" .(A horrific ephemism for casualties incurred outside an attack).  And the years 1909-1917 saw us experiment with some fascinating helmets,  Obviously drawing on crusading knights and Spanish Morrions for inspiration, the quartermaster department tried to come up with a thing that could weigh lightly enough to be worn continually, cool enough to be "comfortable", not impinge rifle fire, allow the rapid donning of gas masks, not blind the wearer, and even save the head from shrapnel and deflect bullets.  

if adopted the iconic look of the US GI would have been forever different, though if you look carefully you can almost see it's evolution into the classic US GI pot helmet of WW2 through Viet nam.

of course congress tossed the whole thing out and went with the tin soup plate bought en masse from british factories,(excepting the  "colored" units that were issued the french Adrian's when they were loaned to the French sectors so they did not have to billet with american white men).