BLU-109 / BLU-116 / BLU-118 / BLU-137 (GBU-24/27) | Specs
BLU-113 / BLU-122 (GBU-28) | Specs
GBU-57 Massive Ordnance Penetrator (MOP) | Specs | Video
GBU-43 MOAB "Mother of All Bombs" | Specs
High Velocity Penetrating Weapon (HVPW)
GBU-72 Advanced 5K (A5K) Penetrator
The Nuclear Option?
Research and Sources
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The wide use of reinforced concrete marked a revolution in protecting man-made structures. Reinforced concrete contains steel reinforcement (typically in the form of steel bars) to increase its strength. With a compression strength rating of usually 5,000 pounds per square inch (PSI) (34.5 MPa) the material can withstand forces that ordinary concrete can't cope with.
An arms race between bunker builder and weapon designer has broken out in modern times with bunkers and tunnels being built deeper below the surface and equipped with thicker layers of reinforcement. In response there have been a series of evolving weapons designed to nullify that advantage. From the 1980's era BLU-109 'HAVE VOID' penetrator, to the legendary GBU-28 "Deep Throat" and up to the GBU-57 Massive Ordnance Penetrator (MOP) weapons have tried to keep pace. New 'bunker busters' are coming along like the High Velocity Penetrating Weapon (HVPW) and the Advanced 5K (A5K) Penetrator which offer a serious bunker busting capability to existing and future aircraft. Improvements in technology such as smart fuses that can count the floors and find the void that is the bunker's interior space have also improved lethality.
A new type of ultra-high-performance concrete (UHPC) - made by combining pure powdered quartz with a mixture of metals and nanofibers - has a compression strength potentially as high as 30,000 psi (207 MPa). This could be a real challenge as it renders most existing bunker busters useless against it. New manufacturing techniques and composite bomb cases made of super materials with ultimate tensile strengths greater than 400 ksi (2750 MPa) show a way forward on this front. Remember that not every protected structure will be hundreds of feet deep and topped with tons of reinforced concrete. Any war presents a variety of hardened targets in which even older weapon designs such as the BLU-109 can make meaningful contributions.
America's adversaries have at least 10,000 hardened and deeply buried targets (HDBT) according to the Defense Intelligence Agency (DIA). Many of these are tactical in nature with a 'cut and cover' design featuring structural overburden equivalent to less than 10 ft (3 m) concrete thickness. But, HDBT exist with 65 to 330 ft (20 to 100 m) equivalent concrete structural overburden and often have a strategic function such as command and control or conceal weapons of mass destruction.
Key targets in any future conflict with Iran, North Korea or China include command / leadership bunkers and nuclear weapons / facilities. In Iran, for example, the Fordow uranium enrichment facility is buried deep underground to deter attacks. This might be a job for the GBU-57 Massive Ordnance Penetrator (MOP) while less powerful weapons could take on the main enrichment site at Natanz.
National Research Council 2005. Effects of Nuclear Earth-Penetrator and Other Weapons.
Washington, DC: The National Academies Press.
ksi (kilopound per square inch) is a unit derived from psi, equivalent to a thousand psi (1000 lbf/in2). Used in materials science, where tensile strength is measured as a large number of psi.
GBU-24/109 detonates after penetrating the ground
Compared to a 2,000 lb (907 kg) MK 84 general purpose bomb the BLU-109 (Bomb Live Unit 109) features a much narrower shape made of high strength steel. This allows the weapon to penetrate the target before a fuse detonates the warhead. Project HAVE VOID produced the BLU-109 in 1985 and it's the basis for a number of different weapons such as certain variants of the GBU-15, GBU-24, the GBU-27, GBU-31 JDAM, and AGM-130.
Used in Desert Storm (the Gulf War) with much success by F-117 Nighthawks, the GBU-27 laser-guided bomb (LGB) is a BLU-109 warhead with a modified GBU-24 Paveway III nose seeker and a 'clipped' tail fin unit - in order to fit in an internal weapons bay of the Stealth Fighter. All 739 GBU-27s used in the Gulf War were dropped by F-117s. Many of these were deployed against bunkers and hardened aircraft shelters (HAS) designed to withstand anything less than a nuclear explosion by German, French, British and Yugoslavian experts. The BLU-109 in the form of GBU-24/109 and GBU-27 LGBs were more than up for the task except for a few super hardened targets. These were subsequently attacked with the GBU-28. The Nighthawks in Desert Storm carried two 2,000-pound GBU-27s, two 2,000-pound GBU-10s, or any combination of the two. On some missions they carried 500 lb (227 kg) GBU-12 LGBs instead - which actually turned out to be pretty effective against certain targets.
Lockheed Martin was contracted by the Air Force in 1995 to develop the Advanced Unitary Penetrator (AUP) BLU-116 as an upgrade to the BLU-109 (I-2000). The AUP has more than twice the penetration of the BLU-109 and because it has the same weight, size, and shape of the BLU-109 it can be used in its place.
Penetration capability is directly proportional to the warhead's sectional density - its weight divided by its cross section. What this means is that more weight delivered over a given or smaller area yields better results. The Advanced Unitary Penetrator achieves this by using an elongated narrow diameter case made of super strong nickel-cobalt steel alloy. The AUP warhead is covered with a lightweight aerodynamic shroud which strips away from the heavy internal penetrator when the weapon strikes the target. As the AUP goes on to penetrate a Hard Target Smart Fuse (HTSF) or equivalent detonates the explosive payload of 240 lb (109 kg) at the optimal point within the target to inflict maximum damage. A limited number of BLU-116s were used in Operation Allied Force (the NATO bombing of Yugoslavia March 24 - June 10, 1999.)
The BLU-118/B uses the BLU-109 penetrator body but with ~560 lb (254 kg) of an advanced explosive with thermobaric properties instead of the standard filling, creating higher sustained blast pressures in tunnels, caves and other confined spaces. This thermobaric fill is made up of a US Navy insensitive explosive called PBXIH-135, and HAS-13, or solid fuel air explosive (SFAE). Fusing is provided by a FMU-143J/B, modified with a new booster and a 120-millisecond delay. The BLU-118's body can be fitted with a variety of guidance system packages, including the GBU-15, GBU-24, GBU-27, GBU-28, and the AGM-130. In this case, it was attached to the GBU-24 guidance and control kit and given the designation GBU-24H/B. The Air Force launched the first BLU-118/B bomb on March 3, 2002 in Afghanistan from a F-15E Strike Eagle. Unfortunately the munition struck a ridgeline that partially obscured the cave entrance target.
A new weapon called the BLU-137 Advanced 2,000 Pound Penetrator (A2K), made of USAF-96 steel and featuring improved fusing and survivability of the bomb components during impact is in production. This greater reliability ensures that the BLU-137 will detonate successfully after punching through concrete and other hard materials. Unlike other high-strength metals which contain expensive elements like tungsten and cobalt, USAF-96 is free of these plus it has a nickel content less than or equal to just 1.5 percent. The BLU-137 is on track to become the standard 2,000 lb (907 kg) class bunker buster over the BLU-109.
Click here to see specification tables.
The 5,000 lb (2268 kg) GBU-28 was made ready in an extraordinarily rapid fashion for a new weapon system. By re-purposing old artillery barrels as bomb cases and using off-the shelf components, in just a matter of weeks it was designed, developed, tested and used in combat. Such was the need to have a weapon to put at risk the most hardened of Saddam's bunkers as there were reports that the 2,000 lb (907 kg) GBU-27 bombs dropped by F-117s were not making much of an impression against them. Some of the command and control bunkers in Baghdad were thought to be buried up to 50 ft (15 m) below the surface, with 2 ft (0.6 m) thick concrete slabs covering a series of interconnected concrete-lined tunnels and chambers.
The night of February 27/28, 1991 saw two F-111Fs, carrying one GBU-28 each, on a special mission out of Taif, Saudi Arabia. The targets were two command bunkers close to the Al Taji air base, northwest of Baghdad. The first weapon fell just wide, but the one from the second aircraft was a direct hit, destroying the primary target and its occupants quite effectively. Strike video showed a large plume of smoke emerge from the bunker's air vents six seconds after impact. This indicated a massive explosion had taken place deep inside the structure.
The GBU-37/B GAM (Global Positioning System Aided Munition), an interim weapon for the B-2 Spirit, utilizes the BLU-113/B which contains about 600 lb (270 kg) of Tritonal.
In 45 sorties B-2s dropped 652 JDAMs and 4 'bunker busting' GBU-37 5,000 lb (2268 kg) bombs during Operation Allied Force (the NATO bombing of Yugoslavia.) With synthetic aperture radar (SAR) the B-2 bomber can eliminate the largest target error source in JDAMs - the error in the exact location of the aim point in GPS space. As part of this process two successive images of the target are taken during initial approach using SAR. The improvement in accuracy proved substantial with the average miss distance of the JDAMs dropped by B-2s being less than half the 40 ft (13 m) for unassisted JDAMs.
Production started in 1999 on the GBU-28B with GPS/INS guidance added to the existing laser seeker for all-weather targeting. The weapon was further improved in 2005 when the BLU-113 was replaced with a BLU-122 warhead made of Eglin steel (ES-1) for greater penetration. Designated the EGBU-28C/B or GBU-28C/B its also known as an Enhanced Guided Bomb Unit.
Source on GBU-28 use: "F-111 & EF-111 Units in Combat" by Peter E. Davies, Osprey publishing (ePub edition), 2014
Source for info on B-2 and Kosovo: "NATO's Air War for Kosovo - A Strategic and Operational Assessment" by Benjamin S. Lambeth, RAND (ePub edition), 2001
Click here to see specification tables.
A 30,000 lb (13608 kg) class weapon, the Massive Ordnance Penetrator (MOP) is a strategic hard target penetrator. It's so heavy that only the B-2 Spirit is tasked to carry it, although B-52 bombers have been used in some of the drop and flight tests. The B-2 bomber can carry two of the MOPs at a time. The new, slightly smaller B-21 Raider should be able to carry one. The 15-ton MOP is even bigger than the "Mother of All Bombs" - although the MOAB contains more explosive.
The MOP's penetration ability is 200 ft (61 m) of 5,000 pounds psi (34.5 MPa) reinforced concrete, 26 ft (8 m) of 10,000 psi (69 MPa) reinforced concrete or 130 ft (40 m) of moderately hard rock. This is a huge improvement over the previous heavy weights - the 5,000 lb (2268 kg) GBU-28 and GBU-37 - which top out at about 20 ft (6.1 m) of 5,000 psi (34.5 MPa) reinforced concrete.
The warhead case is made from a special high-performance steel alloy and encloses a large explosive payload of 5,740 lb (2604 kg) - a mix of AFX-757 and PBXN-114. The steel alloy allows the penetrator to maintain its structure during impact. No doubt the MOP is built with a void sensing fuse to successfully destroy the key space in a bunker and since there's a risk of over-penetration against some targets. This weapon is clearly built for a specific mission: to put at risk deep bunkers and tunnels - the ones containing weapon of mass destruction (WMD) facilities or command and leadership elements. To achieve this it might be necessary to drop one after another MOP at the same deeply buried target.
In October 2014, the Air Force successfully completed one weapon drop from the B-2 aircraft on a representative target. The test took place at the White Sands Missile Range in New Mexico. More recently, in May of 2019, a B-2 bomber released two Massive Ordnance Penetrators in a demonstration / training flight at White Sands. There are at least 20 of these huge GPS-guided weapons. Boeing is the contractor.
The Massive Ordnance Air Blast or MOAB also called the "Mother of All Bombs" is a real monster. It isn't a penetrating weapon like the Massive Ordnance Penetrator (MOP) but its tremendous blast can incinerate and collapse tunnels throughout a large area with a thermobaric explosive warhead. And the MOAB is almost all explosive with 18,700 lb (8482 kg) of its 21,600 lb (9798 kg) weight given over to H6 - a mixture of RDX (cyclotrimethylene trinitramine), TNT, and aluminum - which is 1.35 times more powerful than TNT.
The Air Force Research Laboratory Munitions Directorate (AFRL/RW) developed the MOAB as an improved replacement for the unguided 15,000 lb (6804 kg) BLU-82 'Daisy Cutter' famously used in Vietnam and also in Afghanistan. In a remarkable ten months the MOAB went from development contract to delivery in operational theater (Southwest Asia) for the invasion of Iraq in 2003. The weapon is designed to be deployed from the ramp of a MC-130 Combat Talon II or "Slick" C-130 aircraft without a parachute and uses the KMU-593/B GPS/INS unit for guidance. Set to explode 6 ft (1.8 m) above the ground the MOAB maximizes the effectiveness of the blast wave which reportedly extends out for a mile (1600 m) in all directions.
Even though it achieved initial operating capability (IOC) in 2003 it wasn't used in combat until April 13, 2017. A single MOAB was dropped on an ISIS cave complex in Achin District, Nangarhar Province, Afghanistan. It was reported two days later by a spokesman for the Afghan Army that 94 combatants had been killed in the blast including four commanders with no civilian casualties. Although this was disputed by a member of the Afghanistan parliment who said he heard from people local to Nangarhar that a teacher and his son were killed as well (it's unknown whether this was ever confirmed by US authories.)
The High Velocity Penetrating Weapon (HVPW) is a design for a solid rocket boosted 2,000 lb (907 kg) class 'bunker buster' with the penetration of a 5,000-pound (2268 kg) gravity dropped bomb. Intended to fit in the weapons bay of a F-35 the program began in 2011. The HVPW includes a rocket to propel the weapon deep into the earth at speeds greater than what can be achieved with gravity alone. This is how it can have the impact of a much bigger weapon like the GBU-28. After it enters service it's anticipated that the HVPW will be integrated on a wider range of aircraft than just the F-35. Boeing is the contractor.
Raytheon has researched technology for the program in which the HVPW will be able to succeed even when GPS signals are degraded or unavailable and penetrate at impact angles that will maximize destruction of hardened, buried targets. Work on anti-jam GPS, 'angle of attack' sensing, guidance law and autopilot, and RF (radio frequency) seeker and guidance techniques are intended to give the High Velocity Penetrating Weapon great accuracy and lethality.
A 5,000-pound (2268 kg) class weapon with a BLU-138 penetrator as warhead and a modified JDAM GPS tail kit from a GBU-31, development on the A5K began in 2017. Intended to replace the GBU-28 and be far more lethal the GBU-72 can be used by both fighter and bomber aircraft. It has a ruggedized electronic fuse that can activate at a pre-programmed point inside the target.
Over the Eglin Air Force Base range on Oct. 7, 2021 a 96th Test Wing F-15E Strike Eagle successfully released a GBU-72 Advanced 5K Penetrator at 35,000 feet (10668 m). Operational testing is planned for 2022. Developed by Applied Research Associates, Inc. (ARA)
While the B61-11 earth penetrating nuclear bomb has a yield of 10 - 340 kilotons, the new B61-12 offers a possible solution to extremely tough and high value targets with a yield as low as 0.3 kt (equivalent to 300 tons of TNT). It could be claimed after using such a weapon that a hypothetical really huge conventional bomb would have done the same amount of damage, so it's no big deal. Although, it's doubtful the enemy or the World will see it that way. Many feel that there is "no such thing as a tactical nuclear weapon." It should also be remembered that one or more Massive Ordnance Penetrators (MOP) could take out many deeply buried targets without resorting to nukes. But in the strategic view, it's also necessary to maintain MAD (Mutual Assured Destruction) with our nuclear adversaries. This includes putting at risk leadership and command elements, and these deepest of the deep bunkers can only reliably be put at risk with a nuclear weapon. The F-15E became the first type certified to deliver the B61-12 nuclear bomb on June 8, 2020. Testing to certify the B61-12 on additional aircraft types continues.
Type: Air-dropped thermonuclear bomb
Design: Two-stage radiation implosion
Contractor: Los Alamos National Laboratory (weapon); Boeing (guided tail kit)
Weight: ~825 lb (374 kg)
Diameter: ~13 in (0.33 m)
Length: 11 ft 8 in (3.56 m)
Penetration: The B61-11 can penetrate frozen soil to a depth of (10 - 20 ft) 3 to 6 meters. The B61-12 also has a penetrating capability.
Guidance: Inertial Navigation System (INS)
Accuracy: Improved over other B61 variants, which are unguided.
Price: $28 million each
Estimated Yield: Selectable with four options 0.3kt, 1.5kt, 10kt, and 50kt (the city of Hiroshima was destroyed with a roughly 15 kt airburst.)
Bulletin of the Atomic Scientists - Nuclear notebook. "The B61 family of nuclear bombs" by Hans M. Kristensen and Robert S. Norris, 2014
For more info on nuclear weapons including the Short Range Attack Missile
|Designation||GBU-57 MOP||GBU-43/B MOAB||GBU-28 Paveway III||GBU-24 Paveway III|
|Type||Deep Earth 'Bunker Buster'||Area Blast Weapon||'Bunker Buster'||'Bunker Buster'|
|Design / Manufacturer||Boeing||AFRL; Dynetics||Raytheon||Raytheon|
|Cost||~$3.5 million each||$170,000 each||~$100,000 each||~$85,000 each|
|IOC||November 2011 ?||April 2003||1991||1986|
|In Combat||-||April 13, 2017||Feb. 27/28, 1991||1991|
|Propulsion||None (Free Fall)||None (Free Fall)||None (Free Fall)||None (Free Fall)|
|Guidance||GPS||GPS/INS||Laser, GPS, INS||Laser, GPS, INS|
|Warhead||BLU-127C/B ?||BLU-120/B||BLU-113 or BLU-122||BLU-109|
|Warhead Weight||5,740 lb (2604 kg)||18,700 lb (8482 kg) H6||~600 lb (270 kg) Tritonal||535 lb (243 kg) Tritonal|
|Total Weight||27,125 lb (12300 kg)||21,600 lb (9798 kg)||~5,000 lb (2268 kg)||2,348 lb (1065 kg)|
|Span||?||10 ft (3.05 m)||?||6.7 ft (2.04 m)|
|Length||20.5 ft (6.25 m)||30 ft (9.14 m)||approx. 20 ft (6.1 m)||14.4 ft (4.4 m)|
|Diameter||31.5 in (0.8 m)||40.5 in (1 m)||15 in (0.38 m)||18 in ( m)|
|Penetration||200 ft (61 m)||nil||18 - 20 ft (5.5 - 6 m)||4 - 6 ft (1.2 - 1.8 m)|
|Range||?||3.45 miles with GPS||> 5.75 miles||> 11 miles|
|Integration||B-2A||MC-130H||B-2A, B-52, F-15E||B-52, F-15E, F-16C/D|
|1||H6 is a mixture of RDX (cyclotrimethylene trinitramine), TNT, and aluminum. And is 1.35 times more powerful that TNT (MOAB)|
|2||Penetration is of concrete reinforced at 5,000 pounds per square inch (PSI) (34.5 MPa)|
|3||The B-2 bomber can carry two of the GBU-57 MOPs at a time.|
|4||F-111F carried the GBU-28 also but the aircraft type retired from service in 1996.|
|5||Air Force Research Laboratory (AFRL)|
|6||Also dropped from B-52s conducting tests (MOP)|
Estimates vary by source.
Specifications info mainly from USAF Almanacs.
|Type||Hard Target Penetrator|
|Initiated||1985 as project HAVE VOID||2003||2015 ?||1995 ?|
|Case||4330 modified steel||Eglin steel (ES-1)||USAF-96 steel||Air Force 1410|
|Tensile Strength||245-255 ksi (1690-1758 MPa)||250-260 ksi (1725-1800 MPa)||245 ksi (1690 MPa)||?|
|Warhead||535 lb (243 kg)||~780 lb (350 kg)||?||240 lb (109 kg)|
|Total Weight||1,950 lb (885 kg)||~4,450 lb (2018 kg)||~2,000 lb (907 kg)||~2,000 lb (907 kg)|
|Fuse||FMU-143||?||?||FMU-159/B? or FMU-143|
|Length||7 ft 11 in (2.4 m)||~20 ft (6.1 m)||?||?|
|Diameter||14.6 in (.37 m)||15 in (0.38 m)||in ( m)||?|
|Penetration||4 - 6 ft (1.2 - 1.8 m)||18 - 20 ft (5.5 - 6.1 m)||> BLU-109||> 11 ft (3.4 m) ?|
|Used In||GBU-15, GBU-24, GBU-27||GBU-28||?||?|
|1||H6 is a mixture of RDX (cyclotrimethylene trinitramine), TNT, and aluminum. (MOAB)|
|2||Tensile strengths above are ultimate tensile strengths.|
|3||ksi (kilopound per square inch) is a unit derived from psi, equivalent to a thousand psi (1000 lbf/in2). Used in materials science, where tensile strength is measured as a large number of psi.|
|4||Penetration is of concrete reinforced at 5,000 pounds per square inch (PSI) (34.5 MPa)|
|5||Tritonal is made of a mixture of 80% TNT and 20% Aluminum powder.|
|6||PBXN-109 is a polymer-bonded explosive which is less likely to inadvertently explode compared to Tritonal.|
|7||PBXN-109 is made of 65% RDX, 21% aluminum, and 14% HTPB binder plasticized with DOA.|
|8||AFX-757 an insensitive high energy plastic-bonded explosive, used in the BLU-122.|
|9||AFX-757 consists of 30% Ammonium perchlorate (AP), 33% Aluminum (Al), 25% RDX, and 12% Binders|
|10||BLU-137/B also known as the Advanced 2,000 Pound Penetrator (A2K)|
Material and tensile strength info from an article in "Aerospace & Defense Technology" Magazine Feb. 2021. "More Bang for the Buck: A New Design and Manufacturing Method for Deep Penetrating Bomb Cases" by Dr. Gregory Vartanov, Advanced Materials Development Corp. (Toronto, Canada)
"Desert Storm 1991 The most shattering air campaign in history" by Richard P. Hallion, Osprey publishing (ePub edition), 2022
"F-111 & EF-111 Units in Combat" by Peter E. Davies, Osprey publishing (ePub edition), 2014
"B-2A Spirit Units in Combat" by Chris Davey, Osprey publishing (ePub edition), 2006
"F-117 Stealth Fighter Units of Operation Desert Storm" Warren Thompson, Osprey publishing (ePub edition), 2007
"NATO's Air War for Kosovo - A Strategic and Operational Assessment" by Benjamin S. Lambeth, RAND (ePub edition), 2001
"F-15E Strike Eagle Units in Combat 1990–2005" Steve Davies, Osprey publishing, 2005
"USAF Almanac", Air Force Magazine, 2018 and 2021 Issues.
Air Force Research Laboratory
Air Force Magazine
"Aerospace & Defense Technology" Magazine
Osprey Publishing (Military History)
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