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Operation Carolina Moon
TAWC OPLAN 155
Project 1559

The United States Air Force undertook a special project in late 1965 to develop a method of conducting a stand-off attack against bridges in North Vietnam, many of which were heavily protected by anti-aircraft artillery. The primary target of such an operation was the Thanh Hoa railroad bridge. In September 1965, the Air Force Armament Laboratory (AFATL) undertook development of a floating mine, that could be dropped in the river away from the bridge and detonate when it came into contact with it.

As part of Project 1559, also known as Carolina Moon, AFATL's Technology Branch designed mine with a 6-foot diameter and an approximate weight of 4,000 pounds, of which half was explosive in a focused warhead. The waepon would be dropped from either a C-123 or C-130 aircraft and would feature 2 64-foot parachutes to retard its fall. The mine would have two fuzes. One of these was modified from that used on the CIM-10 BOMARC surface to air missile. The other was an infrared optical fuze. The radar fuze had a cone of 70 degrees, while the optical fuze had a cone of 3 degrees. Work began on fabricating the weapons in October 1965. The steel mine casings were fabricated at the Oak Ridge National Laboratory, an Atomic Energy Commission facility operated by Union Carbide. AFATL's Targets Division designed and built the optical fuzes and the safe-and-arm assembly with parts fabrication by a local contractor. The US Army's Picatinny Arsenal modified 30 BOMARC fuzes and the Air Proving Ground Center assembled the weapons.

In the end, 20 live weapons and another 10 inert items were produced at a cost of $600,000, in addition to wages for personnel working on the project. The final design had a weight of 3,750 pounds, a maximum width of 96 inches, and a maximum height of 31.5 inches. In November 1965, preparations were made for testing of the assembled weapons at Eglin Air Force Base. The subsequent tests covered 4 major objectives: Obtain munition release and ballistic characteristics when extracted from the C-123 and/or C-130 aircraft; evaluate the performance of the fuzing systems and determine the reliability of each system; evaluate the performance of the safety and arming system; and obtain terminal effect data on the munitions. The testing was conducted a shared effort between the Directorate of Armament Development (DAD), the Tactical Air Warfare Center (TAWC), the Special Air Warfare Center (SAWC), and the Air Proving Ground Center {APGC). Parachute riggers were provided by Tactical Air Command (TAC).

During the tests 75 drops were made into water at Eglin Air Force to develop a working rigging design and dropping procedure. The mine's sensors were tested separately in dummy mines against a bridge and the boom of a floating crane. The safe-arm device was found to be successful. No full destruction test of the weapon was conducted at Eglin because of lack of suitable facilities. Test data theoretically estimated an equivalent 1 kiloton blast effect approximately 20-30 feet above the weapon.

Following the tests of the weapon, an initial operation plan was developed on 28 February 1966. TAWC analyzed the proposed operation and concluded that the chances of success were small because the mines, when dropped far enough upstream to avoid effective anti-aircraft defenses, would, run aground. Alternative proposals were said, however, to apparently offer a lesser chance of success and TAWC was directed by Headquarters, US Air Force to develop an operation plan to support the project. On 4 April 1966, TAWC published OPLAN 155, Carolina Moon, in which 2 crews would be trained to conduct the operation using 2 C-130E aircraft. Tactical Air Command would provide the 2 C-130E aircraft, including one equipped with the AN/APN-161 Ka-Band radar system. The aircraft (tail numbers 64-513 and 64-511; the first aircraft being equipped with the specialized radar) were provided by Ninth Air Force through the Commander, 839th Air Division. Command in Chief, Pacific Command ordered the execution of OPLAN 155 on 12 April 1966.

Between 11 April and 15 May 1966, the two crews trained at Eglin Air Force Base for the operation. The training for the 2 crews (a primary and an alternate) included 3 hours of mission orientation (some elements were omitted at this stage), 40 hours of weapon system training, 20 hours of target study, 20 hours of mission planning, 25 hours of day mission training, and lastly 50 hours of night mission training. The last 2 segments involved 2 and 7 weapon drops spectively, and the 2 crews completed a total of 14 drops.

The 2 crews and their aircraft deployed to South Vietnam at Da Nang Air Base on or about 19 May 1966. There they recieved additional target information and participated in final selection of the missino profile. On 20 May 1966, Command in Chief, Pacific Air Forces ordered the execution of Operation Carolina Moon by Seventh Air Force. Seventh Air Force established a plan for conducting the operation on 26 May 1966 and issued a frag order on 28 May 1966 for the first mission.

The first mission was conducted on 29 May 1966. Both aircraft were sortied, with the second acting as an airborne spare. After the first aircraft successfully reached the mouth of the Song Ma River, the second aircraft was recalled. The first aircraft flew at 100 feet AGL toward the target, with the planned release point of 12,000 feet short of the Thanh Hoa bridge. A proviso had been inserted into the frag order that said that if the anti-aircraft fire was light the aircraft could continue another 5,000, releasing the weapon 7,000 feet short of the span. The aircraft recieved light fire and proceeded to the 7,000 foot release point, popping up to 400 feet AGL for thirty seconds prior to the release. After releasing 5 weapons, the aircraft returned to the previous altitude and departed the area. A flight of 4 F-4C aircraft were tasked to conduct a diversionary strike 15 miles south of the bridge as well. Both the C-130E aircraft and the F-4C flight reported heavy anti-aircraft fire in the vicinity of the bridge during the operation. The crew of the C-130E reported that the mission had been a success, but subsequent bomb damage assessment showed no damage to the bridge.

Concerns about appropriate river flow rate and about compromising the objectives of the operation led to the decision to launch a second strike immediately following on 30 May 1966. The ingress route was changed for the second mission, but the final run remained the same. At 0850 on 30 May 1966, Seventh Air Force reported that an F-4C had been lost south of the Thanh Hoa bridge and that this was one of the aircraft involved in a second diversionary strike related to Operation Carolina Moon. At 1103, Seventh Air Force reported that the Carolina Moon C-130E was missing. The members of the diversionary strike (callsign Neon) reported that they had witnessed heavy anti-aircraft fire in the vicinity of the Thanh Hoa bridge at around 0200 on 31 May 1966 during their mission, followed by a large ground flash. The Carolina Moon C-130E was never heard from again, but it was unofficially believed that it had arrived in the target area and had been shot down. The official time of loss was set at 1812 on 30 May 1966. Seventh Air Force reported that Operation Carolina Moon had concluded on 1 June 1966 following the loss of one of the aircraft and its crew.

Interrogation of a North Vietnam torpedo boat crewman some time later reportedly contained information about the first Carolina Moon mission. The individaul reportedly admitted to having seen a US aircraft drop 5 objects into the river near the Thanh Hoa bridge and that 4 of the 5 devices had detonated.




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