When I was in service 1955-57, no hearing protection was issued. Only after that was there concern about hearing loss and it was not until the late 1960's that any form of hearing protection was issued on the rifle ranges.
Actually, the firing of one's own rifle is not especially hard on the ears. But the blast from a rifle to the side or slightly behind can be very damaging.* In combat, of course, the situation is different. The need to hear commands and locate enemy fire is far more important than concern about future hearing loss. There have been devices that supposedly blocked the sound of firing without reducing normal hearing (the Lee-Sonic Ear Valve was an early example), but if the military has issued or is now issuing them, I have not heard of it.
*Ronald Reagan blamed his hearing loss on a blank fired beside his head when making a Western movie, and I have almost total loss of hearing in my left ear due to a .32 Walther PP fired a few inches from my ear.