Here is the next episode, these are infantry bunkers armed with anti tank guns and machine guns and are located in woodland near Kembs forming a second line of defence. The first was easy to spot in a builders yard. Locked barred gate on the outside. Photo 4 shows the outside of the grenade chute, the occupants could launch grenades down the chute at anyone attacking the bunker without fear of being shot at. Plenty of these clever devices in the later photos.