This picture has many interesting things. Telephone and power poles heavy with lines and cables. Two antenna for radio communication says this is a command bunker. The shipping and storage boxes of 40mm shells fired by a Duster replace sandbags as protective cover. Unless the bunker has a/c it will be hot inside. Paper work is created and filed in bunkers like these, so human sweat is a major danger inside a bunker (little air flow) standing in the Vietnam sun and heat.