Hanoi anti aircraft installation

In early 1973 our C-130 was one of the first USAF aircraft to fly into Hanoi following the ceasefire. Our mission was involved with transporting peace negotiation delegates. As we approached Gia Lam Airport, here is a photo of one of the many antiaircraft installations that made Hanoi the most heavily defended city in the world. Only weeks earlier this ring of defense had been highly active during the 1972 Linebacker II Christmas bombing campaign. We certainly would have been a sitting duck at that time. Don't know much about these facilities and whether it was SAM related and/or artillery.