The B-17 Flying Fortress waist gunners were in a very exposed position on the aircraft. It's not like the other crew members were not exposed, it's just that the waist gunners had to stand right in the opening of the fuselage for all to see. And they had to deal with the freezing wind blowing in on them.
Aside from their responsibilities of manning the machine guns, they were the eyes for the crew to announce any incoming aircraft and to give any details concerning their own aircraft in formation. They also assisted with first aid and repairs at the aft end of the plane being it was difficult for anyone forward to work their way back.
They wore layers of clothing along with a heated flight suit to protect from the -50 degree temperatures at 30,000 feet. Ice was a concern if it blocked the oxygen masks. As gunners, they manned .50 caliber machine guns that had just a ring and ball sight so they pretty much had to have good sight alignment to be accurate.
Later model B-17's had an improved sight.Earlier model aircraft had the two waist gunner's right across from each other which made for getting in each others way a problem. Later models off set the positions to alleviate this problem. As enemy pilots learned to attack the flying fortress from the front the waist gunners were not able to get off as many shots as in earlier days and when they did it was as the enemy quickly flew past.
Waist Gunners on The Flying Fortress