27 January 2011

The First Successful Combat Drops of Laser-Guided Bombs

Capt. Thomas Messett led the first combat LGB drop
By 1972 President Richard Nixon's policy of "Vietnamization" was underway as the bulk of responsibility for the defense of South Vietnam transferred from US forces to the South Vietnamese military. Nearly the bulk of US forces in Vietnam had already departed and the Seventh Air Force had already sent half of its combat aircraft back stateside. Only two aircraft carriers remained in the Gulf of Tonkin. The North Vietnamese saw the opportunity to win the war via a conventional attack and on 29 March 1972, twelve of North Vietnam's fifteen divisions made a three-pronged invasion into South Vietnam, leaving only one division in North Vietnam and two divisions in Laos in reserve. Within three days of the Easter invasion, South Vietnamese forces were on the brink of collapse. Over the course of the month of April, a massive influx of US combat aircraft striking the advancing NVA was all that prevented the collapse of the Saigon regime. On 8 May 1972 US Navy aircraft mined the approaches to Haiphong harbor and that evening President Nixon addressed the nation to announce Operation Linebacker, the intensive bombing of North Vietnam, to commence on 10 May 1972. With the North Vietnamese having exposed their logistical tail in their multi-pronged invasion of the South, they left themselves open to air attack on their rear. 

On the first day of Linebacker, sixteen McDonnell Douglas F-4 Phantoms of the 8th Tactical Fighter Wing "Wolfpack" based at RTAFB Ubon in Thailand armed with 2,000 lb electro-optically guided bombs attacked the Paul Doumer Bridge that linked the port city of Haiphong with the capital of Hanoi over the Red River. The weapon systems officers (WSOs) in the back seat of the Phantoms used a TV screen to display the image from the TV camera in the nose of the bomb. Picking out a sharp contrast point between light and dark, the WSOs selected the aim points on the bridge and the bombs were on their way after the dropping aircraft turned for safety. Every electro-optical bomb missed, with the bombs locking on the shadow of the bridge on the water below or suffering a guidance unit failure. Some other supporting aircraft scored hits with conventional bombs, but none of the spans had been dropped. 

The AN/AVQ-10 Pave Knife, showing the camera/laser aperture
While the first laser-guided bombs were under development prior to the 1968 bombing halt, continued work by Texas Instruments had improved the method from the hand-held "Zot Box" that was used by the WSO while the Phantom flew a pylon turn around the target to podded systems in the form of the AN/AVQ-10 Pave Knife that allowed more flexible attack approaches to be made. The WSO used the laser in the Pave Knife pod to designate the target point for the laser-guided bombs. The 8th TFW at Ubon had six Pave Knife pods and it was decided to use them on the next day to revisit the Paul Doumer Bridge. Compared to the sixteen aircraft from the previous day, on 11 May 1972 only four F-4D Phantoms led by Captain Thomas Messett (who flew in the previous day's raid) would attack the bridge. One Phantom carried two 3,000 lb LGBs and the other three Phantoms carried two 2,000 lb LGBs. Only Captain Messett's F-4 carried a Pave Knife pod. The defenders of the bridge didn't think the four Phantoms were the main strike force and as they dived on the bridge, Messett and his WSO designated target points on the bridge and all eight bombs scored direct hits on the bridge, dropping the entire span on the Hanoi side of the bridge into the Red River. It would be a year before the Paul Doumer Bridge was usable again. 

The 3,000 lb GBU-11 added fins and laser guidance to the M118 bomb
The other bridge that was crucial to hitting at the North Vietnamese logistical support of the Easter invasion was the Thanh Hoa Bridge, an immensely tough rail bridge nicknamed "Dragon's Jaw" that crossed the Song Ma River and connected the rail shipment points from China to Hanoi. During Operation Rolling Thunder from 1965 to 1968 over 1,000 missions flew against the Dragon's Jaw, not one mission succeeding in bringing its spans down. The USAF even resorted to dropping floating bombs upstream of the bridge to try and bring it down in Operation Carolina Moon. Nothing worked, it was known as the toughest target in North Vietnam.  On 13 May 1972, two days after the Paul Doumer Bridge was dropped, the 8th TFW set out to drop the Thanh Hoa Bridge for good with fourteen Phantoms carrying nine 3,000 lb LGBs, fifteen 2,000 lb LGBs, and forty-eight 500 lb conventional bombs (due to a shortage of laser-guided bombs). Attacking through an intense flak barrage, direct hits by the LGBs put the entire western span of the Dragon's Jaw into the Song Ma River below. Before the end of Linebacker I in October, the Navy flew an additional eleven missions against the bridge and the USAF another two to insure the bridge was out for good. 

Post-strike recon photo of the Paul Doumer Bridge
It was a stunning debut for a new age of precision munitions. When the Pave Knife was used against the Paul Doumer and Thanh Hoa Bridges by the 8th TFW, it was technically still a developmental program and was rushed forward in response to Nixon's order to blunt the North Vietnamese invasion. Twelve pods were built for the testing program. When the preparations for Operation Linebacker started, three pods stayed stateside to continue the testing program. Three pods went to the US Navy for use on specially-wired Grumman A-6A Intruders and six pods went to the 8th TFW at Ubon for use on specially-wired F-4D Phantoms. Two pods were lost over North Vietnam during Linebacker I- the remaining four pods became quite valuable and after Paul Doumer and Thanh Hoa, were used only on the most critical and important targets. The commander of the Seventh Air Force, General John Vogt, reportedly told the pilots of the 8th TFW "Don't come back if you don't have that pod with you when you return!"

Source: The Linebacker Raids: The Bombing of North Vietnam, 1972 by John T. Smith. Arms and Armour Press, 1998, p61-75.

1 comment:

  1. They were dropping LGB's out of Ubon in 1969-70. Why does this article say THIS was the first successful combat drops of LGB's ??? Ithad already been done ....????? Now I'm confused.