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As explosive ordnance and the means to deliver it against enemy fortifications have evolved through the centuries, government and military leaders throughout history have sought increasingly strong facilities in which to establish secure command and control.
Larger and more powerful explosions eventually drove commanders into underground bunkers, creating an endless cycle of deeper and deeper bunkers versus bigger and more powerful "bunker busters" (B/Bs) able to penetrate more layers of dirt and stone, with the more recent addition of re- inforced metals and concrete used in new "hard and deeply buried targets" (HDBTs).
A cheaper defense, used extensively by those who could not counter superior anti-bunker munitions, has been to build such underground centers beneath schools, hospitals, religious centers, or other civilian structures modern nations have become increasingly loath to endanger. Even the most precision weaponry can do little to overcome a human shield of innocents.
Perhaps the best known bunkers of the last century were crucial to one of the most epic conflicts in history. British Prime Minister Winston Churchill directed first the defense of England and then its counter-attacks from the Cabinet War Room bunker beneath London, while in Berlin German Chancellor Adolf Hitler and the Nazi leadership took shelter from Allied bombs in the Führerbunker.
Hitler's bunker was about 30 feet beneath the garden of the old Reich Chancellery building, while Churchill's, located in the basement of what is now the Royal Treasury building, barely qualified as a bunker, even 75 years ago, and was abandoned at the end of World War II as being too vulnerable to direct attack. Unless provided surface coverage by a civilian human shield, neither would be considered for even the lowest-ranking government officials today.
Bigger and faster
Instead, the 21st Century is home to facilities built deep underground or within natural mountains, such as the Cheyenne Mountain, Colo., headquarters of NORAD, built during the Cold War to survive a nuclear attack, and the Iranian Fordow nuclear enrichment complex, perhaps the deepest and most heavily shielded bunker in the world.
Known intelligence about the actual structure and depth of Fordow and a sister facility at Esfahan leave it unclear if even the largest known non-nuclear bomb in the world-the 15-ton Boeing-built Massive Ordnance Penetrator (MOP)-could knock them out of commission.
With other deep bunkers in Iran, China, and elsewhere around the world employing ultra-high-performance concrete and continuing advances in steel and other reinforced metal components, the Air Force has implemented a rush program to upgrade the GBU-57B MOP.
Funded by the Defense Threat Reduction Agency (DTRA), less than 20 percent of the 20-foot long, 30,000-pound MOP's weight is devoted to explosives. The bulk of the weight is part of the MOP's deep penetration design, intended to take the actual munition up to 200 feet below the surface-close enough to blow up the HDBT or create a man-made "earthquake" that would collapse the buried chambers.
According to Boeing Defense, Space & Security program officials, MOP was developed "to hold adversaries' most highly valued military facilities at risk, especially those protecting weapons of mass destruction". The ongoing MOP upgrade program includes:
adjusted fuses to maximize burrowing power, specifically to withstand impact with layers of granite and steel that encase the Fordow nuclear facility;
upgraded guidance systems to improve precision and allow B-2 and B-52H bombers-the only USAF planes capable of carrying it-to drop multiple munitions directly on top of one another, incrementally excavating earthen defenses until one breaks through and destroys the complex; and
high-tech equipment to evade Iranian air defenses en route to the Fordow complex.
While the MOP can deliver more than a ton of advanced thermobaric explosives to the target level, smaller weapons that could be carried by a greater variety of platforms also will require further advances in thermobarics, which generate higher sustained blast pressures in the confined spaces of tunnels and underground facilities.
Traditional deep, highly reinforced bunkers remain a major part of nearly every nation's strategy to defend its most valuable people, research labs, and command, control, communications, and computer (C4) systems. As new technologies have enabled those to go deeper-and thus more difficult to prosecute from the air-many nations also continue working on improved bunker-busting munitions, with next-generation guidance, navigation, control, and fuzing electronics, greater penetration, and more compressed explosives.
The flagship of the Air Force effort to reach that goal is the U.S. Air Force Research Laboratory's (AFRL) High Velocity Penetrating Weapon (HVPW), which is scheduled to complete research and development in 2014. To help achieve that, the FY12/13 budgets were increased for new technologies in fuzing, warhead survivability, anti-jam GPS, terminal seeker, angle-of-attack sensing, and propulsion.
According to AFRL's Munitions Directorate (AFRL/RW), the HVPW will provide improved capability to penetrate hard, deep targets with boosted impact, mature technologies that can be applied to the 2014 Hard Target Munition DP and "buy down" risk with a survivable ordnance package, terminal guidance, and improved propulsion performance. With F-35 internal carriage loadout and able to operate in GPS degraded/denied environments, it also is intended to put more targets at risk, giving battle planners a 2000 pound weapon with 5000-pound class penetration as early as 2014.
Following the HVPW in development of AFRL's HDBT Capability Concept demonstrations through 2020: 2011-2018-Integrated Precision Ordnance Delivery System (IPODS); 2016-2020-Global Strike Penetrating Munition (GSPM); and 2020-Functional Defeat Munition (FDM).
Those support the Munitions Directorate's three-level capability concept to develop conventional ordnance packages tailored to penetrate and defeat difficult targets: Near-term "Conventional Precision Effects on HDBT", midterm "Enhanced Precision Effects on HDBT," and far-term "Novel Precision Effects against HDBT." The near-term and midterm systems incorporate increased target impact velocity compared to current approaches. The far-term concept will utilize innovative techniques to exploit HDBT vulnerabilities, bringing precision effects to bear on the most difficult targets.
The U.S. and Israel are not the only nations trying to resolve the complex issues of upgrading current munitions and developing the next generation, even as they also work to make their own bunkers immune to attack. Perhaps the lead, on both counts, has been taken by the People's Republic of China-in quantity if not quality.
As with much else about the Chinese military and technology, the types and specifications of their deepest bunkers are uncertain. What is known is China has had one of the most extensive bunker programs in the world since the 1950s, most used as underground airfields to protect the PRC's military aircraft.
Until the 1990s, those were largely near-surface structures to facilitate the internal movement of aircraft. Many of the older bases have closed-some turned into public museums-but the concept remains a major part of Chinese military strategy, as they are in Russia and elsewhere around the world. And those with the most to protect are more likely to enhance the number, depth, and penetration protection of bunkers than go to the expense of trying to replace them with new, non-bunker technologies.
The growth and increasing capabilities of bunkers also has led to an increased demand for bunker busters, which serve offensive and defensive requirements. The latter comprises a first strike strategy to diminish an enemy's military capabilities before they can be used. That is especially true with respect to deep super bunkers, such as those protecting Iran's nascent nuclear weapons development program.
In February 2013, amid reports the U.S. was supplying high-end bunker busters to Israel, a senior member of Iran's parliament, Alaeddin Boroujerdi, says Fordow will never be closed because "our national duty is to be able to defend our nuclear and vital centers against an enemy threat."
"It is estimated that around 10,000 HDBTs exist worldwide, guarding countries' highly prized assets," European defense analyst Adam Smith wrote in a 2012 report, entitled "Bunker Busters: An Indispensable Strategic Capability," for the United Kingdom-based Royal United Services Institute for Defence and Security Studies (RUSI).
The vast majority of U.S. research, development, test, and evaluation (RDT&E) on bunker busters falls to the Air Force Research Lab and its numerous components. One of those, the Air Armaments Center (AAC) at Eglin Air Force Base, Fla., is the Air Force contracting agent for such munitions, tasked with acquiring, testing, and moving state-of-the-art battlespace dominance technologies and weapons to combatant commanders (COCOMs).
AAC's HDBT Weapons Roadmap (Notional) identifies a number of near-, mid-, and long-term munitions, including:
Bomb Live Unit (BLU)-121B-A 2,000-pound "skip bomb" featuring an ultra-hard ES-1C steel casing, AFX-757 thermobaric explosive filler that can only be detonated by a fuze (and not when the bomb bounces along the ground in a horizontal attack on the primary bunker weak spot-its entrance doors), and new guidance software;
BLU-122-5000 pounds, with internal components able to survive 10,000 Gs of lateral acceleration and still function at the bunker level;
BLU-109/113;
Hard Target Void Sensing Fuze (HTVSF);
Hard Target Munition (formerly NextGen Penetrator); and
High Speed Penetrator.
The Air Combat Command (ACC) is looking to the HTM to give legacy aircraft, such as the Navy's F/A-18E/F Super Hornet and Air Force F-15E Strike Eagle/F-15K Slam Eagle, all considered Generation 4.5 fighters, and 5th Gen F-22 Raptor and F-35 Lightning II, advanced capability to attack the super bunkers.
"Next-gen weapons need to be more flexible in terms of the types of targets they can address and, in some cases, may need to be smaller without sacrificing intended weapons' effects," ACC's requirements director, Col. Sam Hinote, says. "This will allow our 5th Gen fighters to have a deeper magazine [increased load-out] and more flexible targeting options."
Perhaps as early as next year, the Air Force hopes to begin work on a 1,000-pound penetrator suitable for use in stealthy weapons bays in the next decade. While specifics remain in development, the options are thought to include a 1,000-pound munition using a rocket motor for increased speed, giving it the effect of a 2,000-pound BLU-109 and possibly a 5,000-pound system without a motor.
Fuzing
"For fuzing, linking to real-time information from the network and changing fuzing to meet the needs of the mission, almost to the moment of detonation, the initial breakthroughs already have been made," says Sean Nolan, RUSI military sciences research analyst. "Now it is a matter of refining those and introducing them into the battlespace."
ATK Defense Group is under contract from AFRL to develop the HTVSF to resolve one of the most persistent shortcomings in each generation of munitions developed for the DOD's Hard and Deeply Buried Target Defeat Capability (HDBTDC): Fuzing.
In addition to being able to survive the extreme G-forces to which deep penetrator munitions are subject, the fuze is key to its improved destructive capability and ensuring it detonates at the right time and place. The latter typically is accomplished by calculating the number of "voids" or levels it passes through, combined with a time-delay capability. Without those, the munition could explode too early-or even too late, potentially passing through the target level and detonating tens of yards beneath its goal.
Tests to validate existing fuzes and fuzewells in near-term HDBT munitions have shown serious vulnerabilities in impact survivability. And integrating even near-term munitions into the first next-generation ordnance and flight profiles will require new developments in guidance, navigation and control concepts.
As target impact velocity increases to yet another level in midterm HDBT ordnance, even more advanced microelectronics capable of surviving violent deceleration will be required to adequately harden bunker-busting fuzes. Stronger penetrator casing materials also will be needed to ensure survival of those advanced munitions as they drive through deeper and more heavily reinforced bunker shielding.
"The purpose of this Directorate's HDBT program is to transition these integrated technologies involving the case, explosive fill, fuze, and associated guidance concepts," according to AFRL Sensors Directorate's mission statement. "The intent of this transition is to reduce the design risk in future HDBT air-to-surface munition concepts that will, themselves, eventually translate into the next generation of fielded HDBT weapons."
An agreement in February 2013 for a joint effort by the Navy and Air Force to modernize the FMU-152A/B Joint Programmable Fuze (JPF) is expected to become part of the ongoing MOP upgrade program.
"The reality is that the world we live in is one in which there are people who seek to build weapons of mass destruction, and they seek to do so in a clandestine fashion," Pentagon Press Secretary Geoff Morrell said at the time. "And this has been a capability that we have long believed was missing from our quiver, our arsenal-and we wanted to make sure we filled in that gap."
Guidance and navigation
"For guidance and navigation, industry has been asked to prove the weapons they are building can communicate with the Link-16 system and work with the other assets in the battlespace to be more reactive to real-time data," Nolan says. "That is especially true for systems being integrated into the JSF. The United Kingdom is putting great emphasis on that, including how data is transferred across the network."
A number of new and evolving technologies, some developed outside the Air Force for other types of programs, also may hold answers to the difficult requirements of deep-penetration bunker busters. For example, a hallmark development in weaponry used in the war in Southwest Asia was precision guidance, from long-range cruise missiles to "smart" bombs and, recently, even mortars. While precision-guided munitions (PGMs) on the battlefield are intended to increase lethality with fewer hits required on target-and significantly reduce collateral damage-high precision also is required for effective bunker buster munitions.
Despite their size underground, deep and heavily reinforced bunkers such as Iran's Fordow complex have only small points of "access" that can be targeted by bunker busting munitions. As a result, next-generation systems will require guidance and navigation capabilities just as precise as battlefield PGMs.
At the U.S. Army Research Laboratory's Sensors & Electron Devices Directorate (ARL SEDD), cutting-edge research into quantum sensing is thought to offer new levels of precision sensing for time-keeping, imaging and navigation not possible with current technologies. As with the possible application of those in PGMs, quantum sensing also may offer advances in the HDBT realm.
"Precision imaging is typically limited by the diffraction limit of light," Dr. Qudsia Quraishi, a SEDD physicist at the forefront of quantum sensing research, explains. "Precision navigation for vehicles or planes has limits ranging from thermal fluctuations to, say, GPS-denied environments. And conventional inertial navigation systems have essentially reached a performance plateau."
Quantum sensors are based on small, coherent laser cooled atoms, enabling extremely accurate measurements of changes in gravity or magnetic fields that offer the potential for tremendous performance gains. Such sensors also rely on a phenomenon not seen in conventional sensors.
"Entanglement is a quantum phenomenon that links one quantum system to another in such a way that a measurement of one system affects the results of the other system, even if these systems are physically separated," Quraishi says. "These two quantum systems go through slightly different environments and interfering them with one another gives information about the environment of one path versus the other. Such atom interferometers can, in theory, provide orders of magnitude better performance than conventional technologies."
Raytheon Missile Systems in Tucson, Ariz., which already provides guidance control units for the BLU-122, received an $11 million contract from AFRL in January 2012 to develop GPS-degraded guidance technology for the HVPW, including anti-jam GPS, angle-of-attack sensing and RF seeker.
For long-term systems beyond 2020, placing primary navigation, guidance, and control systems on UAVs or satellites would reduce size, cost, and impact velocity concerns, which, Nolan says, certainly would be of value. "In the near future, the capability [to breach a super bunker] is possible; navigation and control could be done with just a bit more work to attack something such as Fordow," he adds. "The keys are the penetrating capability and fuzing. Whether the technology is sufficient in the short- and medium-term, I'm not sure. At the moment, the capability of penetration and fuzing to do that sort of job almost seems in the realm of science fiction."
The importance of advanced electronics to match other state-of-the-art components in next-generation bunker buster munitions is reflected in how AFRL responds to the vast majority questions on the subject: That information is "Sensitive and/or Classifed" and therefore "Not Releasable." And defense contractors typically refer all questions to AFRL. Even photographs less than 8 or 10 years old are nearly impossible to locate, even on the Internet.
Some details can be gleaned from Air Force and DTRA budget requests, especially the "Budget Item Justification" notations that explain specific line item requests to Congress. In the DOD FY14 President's Budget Submission, DTRA's Justification Book for defense RDT&E went into even greater detail than usual about requests related to bunker buster technology.
"For some hard and deeply buried targets, physical destruction is neither possible nor practical with current conventional weapons and employment techniques. It may be possible, however, to achieve target defeat objectives by denying or disrupting the mission or function of the target facility," the document informed Congress. "Functional defeat, however, requires more information and more detailed analysis of the target... finding and identifying a facility, characterizing its function and physical layout, determining its vulnerabilities to available weapons, planning and executing an attack, assessing damage and, if necessary, suppressing reconstitution efforts and re-attacking the facility."
Another indicator was the "plus up" of AFRL's FY12 and FY13 HVPW budgets to $35 million to further key technologies such as fuzing, warhead survivability, anti-jam GPS, an advanced terminal seeker, angle-of-attack sensing, and propulsion.
The ability of Israel to have a legitimate capability to attack Iranian nuclear bunkers is vital to that nation's national security, according to Nolan, just as the U.S. ability to do the same against North Korean nuclear facilities is vital to the national security of the U.S. and its allies in that region. "If you have a nation-state threatening the U.S., its allies and friendly countries in the region, having the ability to mount a first strike-regardless of legal ramifications, especially if those nations believe they are under threat from nuclear weapons-is mandatory," he says. "And bunker busters are the only real capability to destroy or at least temporarily render such facilities unusable.
"A large part of the capability in this field essentially is 5- to 10-year-old U.S. technology. Some weapons still have three types of fuzes, al- though most new weapons have a single fuze that can be adjusted in-flight from control platforms. The F-35's reliance on a networked battlespace and the probable need to strike deeper targets against serious air defenses will require feeding off real-time data from the network. The ability to redefine the targets and mission of a deep-strike bunker buster is guiding the state of the art in the next two or three years."
Although secrecy makes it impossible to assess the status of new technology development, especially in Russia and China, neither is on par with the U.S., Israel, or Europe, although Russia is known to have some advanced capabilities in fuzing. Guidance and control, however, especially using a live data feed into the weapon in-flight, are far behind the U.S. "Israeli capability-partly U.S., partly indigenous-is very close to the U.S., which certainly has the global lead in those technologies, with Europe near, but more niched. So the U.S. has the most advanced, networked capabilities, while Israeli does have the ability," Nolan says. "As to the Chinese, hearing about their weapons is easy, knowing is not. I think there still will be some targets that will be out of reach in 2020, but it will be a largely fluid situation, where measures and counter-measures keep growing against each other. But given current technologies and trends, the deepest, hardest bunkers will stay a step or two ahead of any bunker buster that may be used against then. But if someone builds a buster with advanced multilevel penetration and fuzing, it might be possible to say there is no bunker it could not penetrate."
B-52 strategic bomber releases a test version of the Massive Ordnance Penetrator (MOP) during a test of the weapon over White Sands Missile Range, N.M. The Massive Ordnance Penetrator (MOP) bunker-busting bomb is shown here in the bomb bay of a B-2 stealth bomber.
A U.S. Air Force F-15E Strike Eagle releases a GBU-28 bunker-busting, 5,000-pound laser-guided bomb over the Utah Test and Training Range during a weapons evaluation test.
A B-2 Spirit bomber from Whiteman Air Force Base, Mo., drops a B61-11 bunker-buster bomb. The Massive Ordnance Air Burst (MOAB) munition is shown during testing.
Guidance and control for bunker-busting munitions - Military & Aerospace Electronics
Larger and more powerful explosions eventually drove commanders into underground bunkers, creating an endless cycle of deeper and deeper bunkers versus bigger and more powerful "bunker busters" (B/Bs) able to penetrate more layers of dirt and stone, with the more recent addition of re- inforced metals and concrete used in new "hard and deeply buried targets" (HDBTs).
A cheaper defense, used extensively by those who could not counter superior anti-bunker munitions, has been to build such underground centers beneath schools, hospitals, religious centers, or other civilian structures modern nations have become increasingly loath to endanger. Even the most precision weaponry can do little to overcome a human shield of innocents.
Perhaps the best known bunkers of the last century were crucial to one of the most epic conflicts in history. British Prime Minister Winston Churchill directed first the defense of England and then its counter-attacks from the Cabinet War Room bunker beneath London, while in Berlin German Chancellor Adolf Hitler and the Nazi leadership took shelter from Allied bombs in the Führerbunker.
Hitler's bunker was about 30 feet beneath the garden of the old Reich Chancellery building, while Churchill's, located in the basement of what is now the Royal Treasury building, barely qualified as a bunker, even 75 years ago, and was abandoned at the end of World War II as being too vulnerable to direct attack. Unless provided surface coverage by a civilian human shield, neither would be considered for even the lowest-ranking government officials today.
Bigger and faster
Instead, the 21st Century is home to facilities built deep underground or within natural mountains, such as the Cheyenne Mountain, Colo., headquarters of NORAD, built during the Cold War to survive a nuclear attack, and the Iranian Fordow nuclear enrichment complex, perhaps the deepest and most heavily shielded bunker in the world.
Known intelligence about the actual structure and depth of Fordow and a sister facility at Esfahan leave it unclear if even the largest known non-nuclear bomb in the world-the 15-ton Boeing-built Massive Ordnance Penetrator (MOP)-could knock them out of commission.
With other deep bunkers in Iran, China, and elsewhere around the world employing ultra-high-performance concrete and continuing advances in steel and other reinforced metal components, the Air Force has implemented a rush program to upgrade the GBU-57B MOP.
Funded by the Defense Threat Reduction Agency (DTRA), less than 20 percent of the 20-foot long, 30,000-pound MOP's weight is devoted to explosives. The bulk of the weight is part of the MOP's deep penetration design, intended to take the actual munition up to 200 feet below the surface-close enough to blow up the HDBT or create a man-made "earthquake" that would collapse the buried chambers.
According to Boeing Defense, Space & Security program officials, MOP was developed "to hold adversaries' most highly valued military facilities at risk, especially those protecting weapons of mass destruction". The ongoing MOP upgrade program includes:
adjusted fuses to maximize burrowing power, specifically to withstand impact with layers of granite and steel that encase the Fordow nuclear facility;
upgraded guidance systems to improve precision and allow B-2 and B-52H bombers-the only USAF planes capable of carrying it-to drop multiple munitions directly on top of one another, incrementally excavating earthen defenses until one breaks through and destroys the complex; and
high-tech equipment to evade Iranian air defenses en route to the Fordow complex.
While the MOP can deliver more than a ton of advanced thermobaric explosives to the target level, smaller weapons that could be carried by a greater variety of platforms also will require further advances in thermobarics, which generate higher sustained blast pressures in the confined spaces of tunnels and underground facilities.
Traditional deep, highly reinforced bunkers remain a major part of nearly every nation's strategy to defend its most valuable people, research labs, and command, control, communications, and computer (C4) systems. As new technologies have enabled those to go deeper-and thus more difficult to prosecute from the air-many nations also continue working on improved bunker-busting munitions, with next-generation guidance, navigation, control, and fuzing electronics, greater penetration, and more compressed explosives.
The flagship of the Air Force effort to reach that goal is the U.S. Air Force Research Laboratory's (AFRL) High Velocity Penetrating Weapon (HVPW), which is scheduled to complete research and development in 2014. To help achieve that, the FY12/13 budgets were increased for new technologies in fuzing, warhead survivability, anti-jam GPS, terminal seeker, angle-of-attack sensing, and propulsion.
According to AFRL's Munitions Directorate (AFRL/RW), the HVPW will provide improved capability to penetrate hard, deep targets with boosted impact, mature technologies that can be applied to the 2014 Hard Target Munition DP and "buy down" risk with a survivable ordnance package, terminal guidance, and improved propulsion performance. With F-35 internal carriage loadout and able to operate in GPS degraded/denied environments, it also is intended to put more targets at risk, giving battle planners a 2000 pound weapon with 5000-pound class penetration as early as 2014.
Following the HVPW in development of AFRL's HDBT Capability Concept demonstrations through 2020: 2011-2018-Integrated Precision Ordnance Delivery System (IPODS); 2016-2020-Global Strike Penetrating Munition (GSPM); and 2020-Functional Defeat Munition (FDM).
Those support the Munitions Directorate's three-level capability concept to develop conventional ordnance packages tailored to penetrate and defeat difficult targets: Near-term "Conventional Precision Effects on HDBT", midterm "Enhanced Precision Effects on HDBT," and far-term "Novel Precision Effects against HDBT." The near-term and midterm systems incorporate increased target impact velocity compared to current approaches. The far-term concept will utilize innovative techniques to exploit HDBT vulnerabilities, bringing precision effects to bear on the most difficult targets.
The U.S. and Israel are not the only nations trying to resolve the complex issues of upgrading current munitions and developing the next generation, even as they also work to make their own bunkers immune to attack. Perhaps the lead, on both counts, has been taken by the People's Republic of China-in quantity if not quality.
As with much else about the Chinese military and technology, the types and specifications of their deepest bunkers are uncertain. What is known is China has had one of the most extensive bunker programs in the world since the 1950s, most used as underground airfields to protect the PRC's military aircraft.
Until the 1990s, those were largely near-surface structures to facilitate the internal movement of aircraft. Many of the older bases have closed-some turned into public museums-but the concept remains a major part of Chinese military strategy, as they are in Russia and elsewhere around the world. And those with the most to protect are more likely to enhance the number, depth, and penetration protection of bunkers than go to the expense of trying to replace them with new, non-bunker technologies.
The growth and increasing capabilities of bunkers also has led to an increased demand for bunker busters, which serve offensive and defensive requirements. The latter comprises a first strike strategy to diminish an enemy's military capabilities before they can be used. That is especially true with respect to deep super bunkers, such as those protecting Iran's nascent nuclear weapons development program.
In February 2013, amid reports the U.S. was supplying high-end bunker busters to Israel, a senior member of Iran's parliament, Alaeddin Boroujerdi, says Fordow will never be closed because "our national duty is to be able to defend our nuclear and vital centers against an enemy threat."
"It is estimated that around 10,000 HDBTs exist worldwide, guarding countries' highly prized assets," European defense analyst Adam Smith wrote in a 2012 report, entitled "Bunker Busters: An Indispensable Strategic Capability," for the United Kingdom-based Royal United Services Institute for Defence and Security Studies (RUSI).
The vast majority of U.S. research, development, test, and evaluation (RDT&E) on bunker busters falls to the Air Force Research Lab and its numerous components. One of those, the Air Armaments Center (AAC) at Eglin Air Force Base, Fla., is the Air Force contracting agent for such munitions, tasked with acquiring, testing, and moving state-of-the-art battlespace dominance technologies and weapons to combatant commanders (COCOMs).
AAC's HDBT Weapons Roadmap (Notional) identifies a number of near-, mid-, and long-term munitions, including:
Bomb Live Unit (BLU)-121B-A 2,000-pound "skip bomb" featuring an ultra-hard ES-1C steel casing, AFX-757 thermobaric explosive filler that can only be detonated by a fuze (and not when the bomb bounces along the ground in a horizontal attack on the primary bunker weak spot-its entrance doors), and new guidance software;
BLU-122-5000 pounds, with internal components able to survive 10,000 Gs of lateral acceleration and still function at the bunker level;
BLU-109/113;
Hard Target Void Sensing Fuze (HTVSF);
Hard Target Munition (formerly NextGen Penetrator); and
High Speed Penetrator.
The Air Combat Command (ACC) is looking to the HTM to give legacy aircraft, such as the Navy's F/A-18E/F Super Hornet and Air Force F-15E Strike Eagle/F-15K Slam Eagle, all considered Generation 4.5 fighters, and 5th Gen F-22 Raptor and F-35 Lightning II, advanced capability to attack the super bunkers.
"Next-gen weapons need to be more flexible in terms of the types of targets they can address and, in some cases, may need to be smaller without sacrificing intended weapons' effects," ACC's requirements director, Col. Sam Hinote, says. "This will allow our 5th Gen fighters to have a deeper magazine [increased load-out] and more flexible targeting options."
Perhaps as early as next year, the Air Force hopes to begin work on a 1,000-pound penetrator suitable for use in stealthy weapons bays in the next decade. While specifics remain in development, the options are thought to include a 1,000-pound munition using a rocket motor for increased speed, giving it the effect of a 2,000-pound BLU-109 and possibly a 5,000-pound system without a motor.
Fuzing
"For fuzing, linking to real-time information from the network and changing fuzing to meet the needs of the mission, almost to the moment of detonation, the initial breakthroughs already have been made," says Sean Nolan, RUSI military sciences research analyst. "Now it is a matter of refining those and introducing them into the battlespace."
ATK Defense Group is under contract from AFRL to develop the HTVSF to resolve one of the most persistent shortcomings in each generation of munitions developed for the DOD's Hard and Deeply Buried Target Defeat Capability (HDBTDC): Fuzing.
In addition to being able to survive the extreme G-forces to which deep penetrator munitions are subject, the fuze is key to its improved destructive capability and ensuring it detonates at the right time and place. The latter typically is accomplished by calculating the number of "voids" or levels it passes through, combined with a time-delay capability. Without those, the munition could explode too early-or even too late, potentially passing through the target level and detonating tens of yards beneath its goal.
Tests to validate existing fuzes and fuzewells in near-term HDBT munitions have shown serious vulnerabilities in impact survivability. And integrating even near-term munitions into the first next-generation ordnance and flight profiles will require new developments in guidance, navigation and control concepts.
As target impact velocity increases to yet another level in midterm HDBT ordnance, even more advanced microelectronics capable of surviving violent deceleration will be required to adequately harden bunker-busting fuzes. Stronger penetrator casing materials also will be needed to ensure survival of those advanced munitions as they drive through deeper and more heavily reinforced bunker shielding.
"The purpose of this Directorate's HDBT program is to transition these integrated technologies involving the case, explosive fill, fuze, and associated guidance concepts," according to AFRL Sensors Directorate's mission statement. "The intent of this transition is to reduce the design risk in future HDBT air-to-surface munition concepts that will, themselves, eventually translate into the next generation of fielded HDBT weapons."
An agreement in February 2013 for a joint effort by the Navy and Air Force to modernize the FMU-152A/B Joint Programmable Fuze (JPF) is expected to become part of the ongoing MOP upgrade program.
"The reality is that the world we live in is one in which there are people who seek to build weapons of mass destruction, and they seek to do so in a clandestine fashion," Pentagon Press Secretary Geoff Morrell said at the time. "And this has been a capability that we have long believed was missing from our quiver, our arsenal-and we wanted to make sure we filled in that gap."
Guidance and navigation
"For guidance and navigation, industry has been asked to prove the weapons they are building can communicate with the Link-16 system and work with the other assets in the battlespace to be more reactive to real-time data," Nolan says. "That is especially true for systems being integrated into the JSF. The United Kingdom is putting great emphasis on that, including how data is transferred across the network."
A number of new and evolving technologies, some developed outside the Air Force for other types of programs, also may hold answers to the difficult requirements of deep-penetration bunker busters. For example, a hallmark development in weaponry used in the war in Southwest Asia was precision guidance, from long-range cruise missiles to "smart" bombs and, recently, even mortars. While precision-guided munitions (PGMs) on the battlefield are intended to increase lethality with fewer hits required on target-and significantly reduce collateral damage-high precision also is required for effective bunker buster munitions.
Despite their size underground, deep and heavily reinforced bunkers such as Iran's Fordow complex have only small points of "access" that can be targeted by bunker busting munitions. As a result, next-generation systems will require guidance and navigation capabilities just as precise as battlefield PGMs.
At the U.S. Army Research Laboratory's Sensors & Electron Devices Directorate (ARL SEDD), cutting-edge research into quantum sensing is thought to offer new levels of precision sensing for time-keeping, imaging and navigation not possible with current technologies. As with the possible application of those in PGMs, quantum sensing also may offer advances in the HDBT realm.
"Precision imaging is typically limited by the diffraction limit of light," Dr. Qudsia Quraishi, a SEDD physicist at the forefront of quantum sensing research, explains. "Precision navigation for vehicles or planes has limits ranging from thermal fluctuations to, say, GPS-denied environments. And conventional inertial navigation systems have essentially reached a performance plateau."
Quantum sensors are based on small, coherent laser cooled atoms, enabling extremely accurate measurements of changes in gravity or magnetic fields that offer the potential for tremendous performance gains. Such sensors also rely on a phenomenon not seen in conventional sensors.
"Entanglement is a quantum phenomenon that links one quantum system to another in such a way that a measurement of one system affects the results of the other system, even if these systems are physically separated," Quraishi says. "These two quantum systems go through slightly different environments and interfering them with one another gives information about the environment of one path versus the other. Such atom interferometers can, in theory, provide orders of magnitude better performance than conventional technologies."
Raytheon Missile Systems in Tucson, Ariz., which already provides guidance control units for the BLU-122, received an $11 million contract from AFRL in January 2012 to develop GPS-degraded guidance technology for the HVPW, including anti-jam GPS, angle-of-attack sensing and RF seeker.
For long-term systems beyond 2020, placing primary navigation, guidance, and control systems on UAVs or satellites would reduce size, cost, and impact velocity concerns, which, Nolan says, certainly would be of value. "In the near future, the capability [to breach a super bunker] is possible; navigation and control could be done with just a bit more work to attack something such as Fordow," he adds. "The keys are the penetrating capability and fuzing. Whether the technology is sufficient in the short- and medium-term, I'm not sure. At the moment, the capability of penetration and fuzing to do that sort of job almost seems in the realm of science fiction."
The importance of advanced electronics to match other state-of-the-art components in next-generation bunker buster munitions is reflected in how AFRL responds to the vast majority questions on the subject: That information is "Sensitive and/or Classifed" and therefore "Not Releasable." And defense contractors typically refer all questions to AFRL. Even photographs less than 8 or 10 years old are nearly impossible to locate, even on the Internet.
Some details can be gleaned from Air Force and DTRA budget requests, especially the "Budget Item Justification" notations that explain specific line item requests to Congress. In the DOD FY14 President's Budget Submission, DTRA's Justification Book for defense RDT&E went into even greater detail than usual about requests related to bunker buster technology.
"For some hard and deeply buried targets, physical destruction is neither possible nor practical with current conventional weapons and employment techniques. It may be possible, however, to achieve target defeat objectives by denying or disrupting the mission or function of the target facility," the document informed Congress. "Functional defeat, however, requires more information and more detailed analysis of the target... finding and identifying a facility, characterizing its function and physical layout, determining its vulnerabilities to available weapons, planning and executing an attack, assessing damage and, if necessary, suppressing reconstitution efforts and re-attacking the facility."
Another indicator was the "plus up" of AFRL's FY12 and FY13 HVPW budgets to $35 million to further key technologies such as fuzing, warhead survivability, anti-jam GPS, an advanced terminal seeker, angle-of-attack sensing, and propulsion.
The ability of Israel to have a legitimate capability to attack Iranian nuclear bunkers is vital to that nation's national security, according to Nolan, just as the U.S. ability to do the same against North Korean nuclear facilities is vital to the national security of the U.S. and its allies in that region. "If you have a nation-state threatening the U.S., its allies and friendly countries in the region, having the ability to mount a first strike-regardless of legal ramifications, especially if those nations believe they are under threat from nuclear weapons-is mandatory," he says. "And bunker busters are the only real capability to destroy or at least temporarily render such facilities unusable.
"A large part of the capability in this field essentially is 5- to 10-year-old U.S. technology. Some weapons still have three types of fuzes, al- though most new weapons have a single fuze that can be adjusted in-flight from control platforms. The F-35's reliance on a networked battlespace and the probable need to strike deeper targets against serious air defenses will require feeding off real-time data from the network. The ability to redefine the targets and mission of a deep-strike bunker buster is guiding the state of the art in the next two or three years."
Although secrecy makes it impossible to assess the status of new technology development, especially in Russia and China, neither is on par with the U.S., Israel, or Europe, although Russia is known to have some advanced capabilities in fuzing. Guidance and control, however, especially using a live data feed into the weapon in-flight, are far behind the U.S. "Israeli capability-partly U.S., partly indigenous-is very close to the U.S., which certainly has the global lead in those technologies, with Europe near, but more niched. So the U.S. has the most advanced, networked capabilities, while Israeli does have the ability," Nolan says. "As to the Chinese, hearing about their weapons is easy, knowing is not. I think there still will be some targets that will be out of reach in 2020, but it will be a largely fluid situation, where measures and counter-measures keep growing against each other. But given current technologies and trends, the deepest, hardest bunkers will stay a step or two ahead of any bunker buster that may be used against then. But if someone builds a buster with advanced multilevel penetration and fuzing, it might be possible to say there is no bunker it could not penetrate."
B-52 strategic bomber releases a test version of the Massive Ordnance Penetrator (MOP) during a test of the weapon over White Sands Missile Range, N.M. The Massive Ordnance Penetrator (MOP) bunker-busting bomb is shown here in the bomb bay of a B-2 stealth bomber.
A U.S. Air Force F-15E Strike Eagle releases a GBU-28 bunker-busting, 5,000-pound laser-guided bomb over the Utah Test and Training Range during a weapons evaluation test.
A B-2 Spirit bomber from Whiteman Air Force Base, Mo., drops a B61-11 bunker-buster bomb. The Massive Ordnance Air Burst (MOAB) munition is shown during testing.
Guidance and control for bunker-busting munitions - Military & Aerospace Electronics
