Slaying the Dragon

The bridge-busting debut of the U.S. Air Force's laser-guided bomb

Slaying the Dragon Slaying the Dragon
We see it every day – video of a “precision” aerial attack on some terror or insurgent group. The ability to put crosshairs on... Slaying the Dragon

We see it every day – video of a “precision” aerial attack on some terror or insurgent group. The ability to put crosshairs on a target and make it disappear has become synonymous with modern warfare.

But this technology is not new. The laser-guided bomb — the grandfather of modern, precision, air-dropped munitions — saw its first use in combat in Vietnam way back in 1972.

The target was the Ham Rong bridge, which translates as “Dragon’s Jaw.” The span also bore the nickname Thanh Hoa after nearby city. It was a big bridge — 540 feet long and climbing to 50 feet over the Song Ma River. The Dragon supported rail and vehicle traffic and was a major North Vietnamese military supply artery approximately 50 miles south of Hanoi. Over-engineered with large concrete abutments and ringed with anti-aircraft guns and surface to air missiles, the Dragon was not to be trifled with.

The Dragon was also the 14th of the 94 targets the U.S. Joint Chiefs of Staff identified by name for the 1965 air campaign.

There were two options for attacking the Dragon by air. Either an attack by precision “guided” bombs or conventional, freefall “dumb” bombs.

The U.S. Air Force made its first attempt at slaying the Dragon on April 3, 1965, sending in F-105 fighterbombers to drop AGM-12 Bullpup radio-guided bombs. The Bullpups with their small, 250-pound warheads literally bounced off.

A follow-on attack the next day involved a staggering 48 F-105s, each carrying eight 750-pound dumb. It was also unsuccessful. The American pilots reported more than 300 hits, but the bridge remained operational.

Desperate, the Air Force developed a third attack option — C-130 cargo planes carrying huge mines designed to be parachuted upriver and float down the Song Ma to explode under the bridge. Operation Carolina Moon kicked off in May 1966. A C-130 successfully delivered five mines, four of which exploded without notable damage to the bridge. A second attack by a C-130 the following night ended with the North Vietnamese shooting down the attacking plane with the loss of the crew. The Air Force abandoned Carolina Moon.

Above — the Dragon in 1972. At top — the bridge after the successful attack. Photos via Wikipedia

 

Through 1968 the bridge had resisted all attacks and at worst was out of action for only a few days, mostly due to collateral damage to the road and rail networks feeding the bridge.

The bombing halt from 1968 to 1971 provided the North Vietnamese with time to reinforce the Dragon. The Pentagon stayed busy, too, working on improved precision-guided bombs. When North Vietnam invaded the South in the spring of 1972 and Pres. Richard Nixon responded with the Linebacker bombing campaign, the Air Force could deploy new precision weapons with warheads planners believed were big enough to take down the Dragon.

There were two new types of munitions — electro-optically guided bombs, or “EOGBs,” and laser-guided bombs, a.k.a., “LGB.” Both had advantages … and disadvantages.

The AGM-62 Walleye EOGB featured a camera in its nose of the bomb that could lock on to a target, allowing the aircraft to launch the weapon and then turn away to avoid flak and surface-to-air missiles. This fire-and-forget capability looked good on paper, but required excellent weather and high-contrast targets to work at ranges that minimized the threat to the attacking aircraft.

Another disadvantage was cost. The Walleye was a single unit and more expensive to produce. In addition, the Walleye II of 1972 had a maximum warhead size of 2,000 pounds. And it was unclear if 2,000 pounds of explosives would get the job done.

The LGBs included a seeker head that sought the energy from a laser beam fired by the attacking aircraft. This required the designating aircraft to “paint” the target during the munition’s flight until it struck the target. The laser seeker and tail fin unit that guided the weapon fit on standard dumb bombs up to 3,000 pounds. Thus the LGB was cheaper and delivered a bigger punch.

Pave Knife. Photo via the author

 

One vital component of the LGB system was a device called “Pave Knife.”

Built by Ford Aerospace, the AN/AVQ-10 Pave Knife targeting pod guided LGBs in a high-threat environment. A key requirement was the ability of the designating aircraft to maneuver defensively during an attack. The first LGBs, initially tested in 1968, required a separate designator aircraft to perform a steady 6,000-foot orbit over the target in order to designate the LGBs launched by other aircraft.

This made the designator an easy target … and made LGBs unsuitable against high-threat targets such as the Dragon.

Pave Knife solved that problem. It consisted of a pod that slung underneath the aircraft. The laser designator was controlled by a crewman using a joystick. A television camera was slaved to the laser so the operator could hold a crosshair on the target and manually designate it. In testing it worked well, but Pave Knife was essentially handmade and only six pods were available in 1972.

The first LGB attack on April 27, 1972 included both Walleye EOGBs and Pave Knife-guided LGBs.

However, low clouds foiled the Pave Knifes. The Walleyes did some damage but were unable to get the job done. It took a follow-on assault on May 13 — involving 14 Air Force F-4 Phantoms carrying Pave Knife and carrying 2,000-pound and 3,000-pound LGBs — to topple the Dragon. The jets struck the bridge multiple times and rendered it unusable. The damage was unprecedented; the western span completely dislodged. The U.S. Navy conducted additional attacks throughout 1972 to delay repair efforts.

The Dragon stayed down until 1973.


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