By Cameron Curtis
Introduction-Guided Bombs
Guided bomb units (GBUs) are extremely effective against static targets. They came into their own during the Vietnam war when they were used to bomb difficult targets like bridges. As time passed, improvements were made to their guidance, and their range was extended. All bombs glide because of their trajectory upon release from the delivery aircraft, but the range of a guided bomb can be extended by the addition of fold-out wings.
In a previous article, Glide Bombs, I described the effectiveness of Russian glide bombs in shattering Ukrainian fortifications. Typically, a US smart bomb, the JDAM, is targeted using GPS guidance. The JSOW (Joint Stand-Off Weapon), is a guided glide bomb with fold-out wings. Russian glide bombs are targeted with GLONASS, the Russian equivalent of GPS.
The problem is that such glide bombs are effective against static targets. To state the obvious, many targets move. Vehicles. Trains. Ships. For such targets, a GPS-guided GBU is not effective. A laser-guided GBU can do the job, but requires either an operator on the ground, or a second aircraft, to lase the target and remain on post until impact. This exposes the element lasing the target to significant risk.
Clearly, it is purposeful to develop guided bombs and glide bombs with seeker heads. Such weapons, once locked on to a target, can self-course-correct to impact.
The Problem of Moving Targets – Guided Bombs with Seekers
On June 21, 1921 bombers of Brigadier General Billy Mitchell’s First Provisional Air Brigade sank the captured German battleship Ostfriesland. The biggest criticism of Billy Mitchell’s achievement was that the ship had no air defense and was not maneuvering. The British proved the concept at Taranto, and the Japanese at Pearl Harbor.
The United States built Stormbreaker, the GBU-53/B 100-lb glide bomb with a seeker head, and tested it on tanks. This warhead, however, is too small to do much damage to a large surface combatant. In an effort to find a low-cost anti-shipping weapon, the US Air Force has developed a seeker head to guide a JDAM or guided glide-bomb to hit a moving target like a ship.
The Air Force Research Laboratory developed a seeker head for the 2,000-pound GBU-31 JDAM. The weapon was specifically designed to sink naval targets. On April 28, 2022 an F-15 successfully sank a target vessel in the Gulf of Mexico (see Figure 1).
The nose plug of the GBU was modified to keep the weapon traveling straight and true upon contact with the water. The trajectory is that of a standard wingless GBU, with GPS guidance in the tail, but with a modified (and classified) seeker head in the nose. The new seeker is designed to guide the weapon to strike the target just below the waterline. That requirement, in itself, suggests impressive course correction upon final approach. As shown in Figure 1, the effect is dramatic. The weapon is intended to do the same job as a submarine-launched torpedo at a fraction of the cost.
The Air Force has its eye on America’s inventory of 300,000 dumb bombs that could be converted to ship-killing GBUs with cheap conversion kits. This video, Golden Horde, discusses the ambition to launch a swarm of target data-sharing GBUs that would force a surface combatant to defend itself against dozens of threats at the same time.
On July 19, 2024 a B-2 Spirit stealth bomber used the weapon to sink the USS Tarawa (Figure 2). The amphibious assault ship was a small carrier that had been decommissioned and offered up for sacrifice as a target ship. The test was successful, but no footage has been released. The significant aspects of the test were the size of the target, and the use of the B-2 stealth platform.
The outstanding question emerging from these tests is what I call “The Billy Mitchell Question.” It’s a compound question, raising two issues.
First, the target ships were moving, but we are not told anything about the degree to which they were maneuvering. One would need to convert the target ships into massive sea drones to direct them to take evasive action. A seeker head designed to strike just below the waterline is going to have a lot of trouble hitting a hard-maneuvering vessel just so.
This video GBU Destroys Target Ship in Gulf of Mexico shows the destruction of the target container ship in the earlier test. Slow it down to .25x-speed and you will see the weapon strikes low on the port side of the vessel. The intent was to strike below the waterline. The angle of attack remains very steep because the GBU-31 used is not a glide bomb. The point I’m making is that the ship is travelling straight ahead. There is no evasive action. The GBU will itself, by definition, have limited ability to maneuver against a hard-turning target.
Second, Billy Mitchell dropped his bombs on an undefended target. Neither target vessel was in a position to defend itself. There isn’t much we can do about the first issue other than acknowledge it. We will deal with the second issue in the following section.
A Weapon for Permissive Environments
This modified GBU-31 must be released from altitude, no further than 40km from its target. That’s because the glide bomb must use the forward motion of the aircraft to set it on its trajectory. The weapon’s payload, release altitude, and the aircraft’s velocity all affect its range and time-to-impact.
The business model for this weapon is predicated on the fact that there are many potential Chinese and Russian target vessels under 1,000 tons displacement that do not have long-range air defense. The argument is made that such ships can be attacked from a range of 40km.
Vessels under 1,000 tons are roughly the size of a coastal freighter. They are numerous and they are low-value targets. Not to mention that such vessels can be convoyed under the protection of a 5,000 ton frigate equipped with sophisticated air defense.
That’s why the Air Force started thinking in terms of strike packages of a dozen aircraft or more, carrying hundreds of bombs. That’s why they considered the “Golden Horde” concept of data-linked glide bombs.
But the optimal defensive solution has never been to shoot dozens of GBUs out of the sky. This isn’t World War II. The solution is to accept the loss of this or that lonesome coastal freighter and defend convoys and high-value targets with heavily armed surface combatants. Russian and Chinese corvettes and frigates are equipped with air defense missiles that can reach out 140km, far beyond the 40km range of a GBU.
The optimal defense is to kill the attacking aircraft.
Stealth and Non-Permissive Environments
In a non-permissive environment, the weapon of choice is clearly a much more expensive, stand-off, low-observable cruise missile or ballistic missile. Unfortunately, these come with their own problems of cost, long production times, and guidance effectiveness against moving targets and ECM.
There is only one way to get the delivery aircraft inside the 40km limit. That is stealth. Both the F-35 and B-2 can deliver the modified 2,000-pound GBU-31. The weapon fits inside their weapons bays without adversely affecting their structural radar cross section. For technical reasons we won’t get into, the B-2 is somewhat stealthier than the F-35.
On its face, a stealth aircraft and the modified GBU make a lethal ship-killer. Undetected, there is little a ship can do to defend against such an attacker.
Long-Wave Radar and China’s Pacific Kill Chain
In my previous SOFREP articles WW2 Radars Can Detect Stealth Aircraft, and The Anti-Stealth Kill Chain: Is the F-35 Untouchable?, I discussed in some detail why all stealth aircraft today are vulnerable to long-wave, low-frequency radars of the type used in the Battle of Britain. I will not review that material here.
What is important is that long-wave radars that operate in the VHF, HF, and KHz regions of the electromagnetic spectrum can detect stealth aircraft. Furthermore, they can detect targets at long ranges of between one thousand and five thousand miles. They do this by bouncing electromagnetic waves off the ionosphere, or by propagating waves over the interface between air and land. The trade-off is that these radars are large (too big for ships), suffer from reduced discrimination ability, and are not well-suited to tracking targets.
To render these long-wave radars effective, they must be networked to other shorter-wave, higher-frequency radars that operate in the S, C, X, and Ku bands. The long-wave radars detect the presence of the threat (immediately negating the element of surprise) and pass the target on to tracking and targeting radars. The latter will engage the target and direct the weapons system to destroy it.
Conclusion
The US Air Force used the B-2 to conduct its test on the USS Tarawa precisely because they recognize that a stealthy delivery platform is needed to render this weapon effective. The Chinese and Russians are not blind to this fact.
Russia has been developing and deploying long-wave radars ever since World War II. It supplied China with that country’s first over-the-horizon radar system and now both countries are racing to develop and deploy sophisticated anti-stealth radar systems with ranges of up to five thousand miles. Crucially, the objective is to network these long-wave radars into kill chains that include shorter-range targeting radars.
Suffice to say that China is blanketing the Pacific with radars and building an anti-stealth kill-chain. Recent business and geopolitical developments in Sri Lanka suggest that China will deploy sophisticated radars on that island. Chinese long-wave radar can dominate the Indian and Pacific Oceans. Search fans can cover the middle east and reach to Hawaii. No B-2 or B-52 landing on or taking off from Diego Garcia will escape detection.
Figure 3 illustrates the coverage of Chinese long-wave radar (operating in the HF-band). This installation is based on Hainan island and already provides extensive coverage. Another on Sri Lanka would provide China with the potential to detect and combat stealthy threats across the Indian and Pacific Oceans.
In a forthcoming article, I will discuss this topic in more detail.
This essay first appeared in SOFREP
Cameron Curtis is the author of the Breed action thriller series, available on Amazon. The stories are adrenaline-fuelled and emotionally engaging. The novels combine credible premises based on current events, technical detail, and propulsive plotting.
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