One of the toughest targets in North Vietnam during the long war there was the Thanh Hoa Bridge over the Song Ma River. The bridge was a massive steel truss and concrete structure that carried a railroad down the center and a two lane road way on each side and was a major supply choke point from Hanoi and the harbor of Haiphong. Crossing the river at its narrowest point, sharp limestone ridges on each side gave it the nickname Ham Rong, or “Dragon’s Jaw” as the American pilots referred to it. Because of its strategic nature on the supply route to the battlefields along the DMZ and to the Viet Cong in South Vietnam, the Thanh Hoa Bridge was a significant target and was recognized as such by the North Vietnamese who protected the area with some of the densest antiaircraft defenses outside of Hanoi and Haiphong.
Despite the initial attacks by F-105s from bases in Thailand, the bridge which was over-engineered, refused to drop. One USAF attack had 79 aircraft of varying times involved at the same time and yet the bridge still stood. Late that year the Armaments Development Laboratory at Eglin AFB in Florida had been doing research on using high-explosive weapons that focused their energy- similar to a scaled up version of a shaped charge used in anti-tank warfare. The command staff of the Pacific Air Forces running the USAF air campaign in Vietnam was notified of the possible destructive power of these new weapons, but they could only be carried by cargo aircraft and the only suitable would be the Lockheed C-130 Hercules. Since the AA defenses of the Thanh Hoa Bridge were so intense, a plan was formulated to have C-130s drop the weapons up river and let them float down to the bridge and detonate. The opeation was given the code name Carolina Moon.
Two experienced crews were chosen from the 314th Troop Carrier Wing at Sewart AFB, Tennessee. One crew was led by Major Richard Remers and the other crew was led by Major Thomas Case, both crews from the 61st Troop Carrier Squadron.
On 30 May 1966, Remer’s crew took off first in a C-130E from Da Nang AB just after midnight local time. With a crew of seven, they flow at 100 feet above the South China Sea and then turned in towards the target area, remaining at 100 feet. There were two navigators aboard Remer’s Hercules and there were two drop zones upstream from the Thanh Hoa Bridge selected. The first one was 2 miles up river and the second one was just a mile up river. Upon reaching the first point and meeting no resistance, Remer pressed on the the next drop point. Soon anti-aircraft gunfire opened up across the river valley but the successfully dropped their five Carolina Moon weapons in the river and flew all the way back to Da Nang on the deck, rarely exceeding 100 feet.
The following day reconnaissance photos showed the bridge still standing so that night, the second mission led by Major Case took off just over a hour after midnight from Da Nang. As with the previous night’s mission with Major Remer, USAF F-4s conducted diversion strikes in the area and one of the pilots reported heavy anti-aircraft fire and large ground flash about 2 minutes before the drop zone for the weapons. Major Case’s crew was never heard from again and it wasn’t until well after the war ended into the present day that the crash site for the Hercules was finally identified with excavations under way.
It was later found that the special bombs did in fact detonate under the bridge as designed, but they simply lacked enough force to bring down the spans of the Thanh Hoa Bridge. It wasn’t until 1972 during the Linebacker missions that F-4 Phantoms dropping brand-new laser-guided bombs (LGBs) managed to finally put the Dragon’s Jaw out of commission.
Source: C-130 Tactical Airlift Missions 1956-1975 by Sam McGowan. Aero Publishers, 1988, p122-124.