Just to add my humble opinion, the two helmets look more like miners helmets to me. The have a much deeper, rounder crown than the WW I doughboy helmets. One of them has a hole in the top that could be there to help attach a miner's light to it. My dad worked in the gold mines in California in the late 1930' until 1942 when the War Production Board closed all the gold mines down as "non-essential" to the war efforts. Also had several uncles work in the gold mines before they went off to war. Just my humble opinion.