Bunker Buster Bombs

 

USA Drops Bunker Buster Bombs on Iran

In June 2025, the 12-day war was fought between Iran Vs Israel/USA (that is because Israel can’t fight any war without blessings and supplies of USA). Israel said Iran was weeks if not months away from building a nuclear bomb; (it’s a different matter that Israel (particularly Netanyahu) has been saying this since past 30 years). In the war, while Iran used land launched missiles and drones; Israel used aircraft dropped bombs and missiles. The war was started ostensibly to destroy Iranian missile and nuclear bomb capabilities. Suddenly, USA directly entered the war on 11th day and dropped 14 ‘Bunker Buster’ bombs on 3 key nuclear facilities of Iran; namely Fordow, Esfahan and Natanz. USA used the frighteningly expensive 7 B-2 bombers (each costing US$2 billion) to drop a total of 14 GBU-57 bunker busters. The 7 B-2 bombers took off from Missouri, USA for a 40-hour non-stop flight to drop bunker buster bombs at Fordow, Esfahan and Natanz; key nuclear enrichment linked sites of Iran.  

While these 7 B-2s dropped bombs from the west, a decoy of 4 more B-2 bombers were deployed from east that took off from Diego Garcia in the Indian Ocean. It is said that USA had just 20 GBU-57 bombs in its inventory before this, so now it presumably has only 8 left in inventory. Even after this though, Iran has said that above ground facilities at Fordow, Esfahan and Natanz have incurred heavy damage but underground facilities are intact and at the most pushed Iran’s nuclear program by a few months only. It is just matter of time when Iran restarts its nuclear enrichment work. In retaliation Iran fired 14 missiles at the Al Udeid Air Base of USA in Qatar after giving prior warning.

So, What Is a Bunker Buster Bomb?

A bunker buster bomb is a type of specially made munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers. These kind of bombs are being made since World War 2, both by Axis Powers and Allied Powers. Some of these are as follows:-

Röchling Armor Piercing Shells

Röchling armour piercing shells were bunker-busting artillery shells, developed by the German engineer August Coenders. These bombs were based on the theory of increasing sectional density to improve penetration. They were tested in 1942 and 1943 against the Belgian Fort d'Aubin-Neufchâteau.

Aircraft Delivered Bombs

In World War II the German Luftwaffe developed a series of unguided rocket-propelled armor-piercing bombs for use against shipping and fortifications. In World War II, the British designer Barnes Wallis, already famous for inventing the bouncing bomb, designed two types of bombs that became the conceptual predecessors of modern bunker busters; the 5-tonne ‘Tallboy’ and the 10-tonne ‘Grand Slam’. These were called "Earthquake" bombs—a concept he had first proposed in 1939. The designs were very aerodynamic, that allowed them to exceed the speed of sound as they fell from 22,000 ft (6,700 m).

The tails were designed with offset fins that caused the bombs to spin as they fell. Using the same principle as a spinning top, this enabled them to resist being deflected, thereby improving accuracy. They had casings of high-grade steel, stronger than the usual World War II bomb so that they would survive hitting a hardened surface, or penetrate deep into the ground. Though called as "bunker busters" today, the original "earthquake" theory was more complex and subtle than simply penetrating a hardened surface.

The ‘earthquake bombs’ were designed not to strike a target directly, but to impact beside it, penetrate under it, and create a 'camouflet', or large buried cavern, as well as deliver a shock wave through the target's foundations at the same time. The target then collapses into the hole, no matter how hardened it may be. The bombs had strong casings because they needed to travel through rock rather than reinforced concrete, though they could perform equally well against hardened surfaces. In an attack on the Valentin U-Boat pens at Farge, two ‘Grand Slam’ bombs went through the 15 ft (4.5 m) reinforced concrete hardening; equalling or exceeding the best current penetration specifications.

The British ‘Disney Bomb’ officially known as "4500 lb [2,000 kg] Concrete Piercing/Rocket Assisted Bomb", or the "Crab" was a World War II device designed to be used against U-boat pens and other super-hardened targets. Devised by Captain Edward Terrell RNVR of the Admiralty's Directorate of Miscellaneous Weapons Development, these bombs had a streamlined hardened case and weighed about 4,500 lb (2,000 kg) including the rocket assembly. However, actual explosive content was just about 500 lb (230 kg) only. For accuracy, these bombs were dropped from a pre-determined height (usually 20,000 ft (6,100 m)). They would free-fall for around 30 seconds till they reach at 5,000 ft (1,500 m), then the rockets were ignited, causing the tail section to be expelled. The rocket burn lasted for just 3 seconds but added 300 ft/s (91 m/s) to the Disney Bomb's speed, giving a final impact speed of 1,450 ft/s or 440 m/s; 990 mph.

Post World War II, the US added a form of remote guidance to the ‘Tallboy’ to create ‘Tarzon’, a 12,000 lb (5,400 kg) bomb that was deployed in the Korean War (1950-53) against an underground command center near Kanggye. Since then the USA developed variety of customized ‘bunker buster’ bombs, including the BLU-109 bombs that are intended to penetrate concrete shelters and other hardened structures before exploding. BLU-109 bombs entered service with USAF in 1985. Its most famous use occurred recently when Israeli F-15I fighter jets reportedly dropped 82 tons of BLU-109s in the strike that killed Hezbollah leader Hassan Nasrallah in Beirut on 27 September 2024.

 

During Operation Desert Storm (1991), there was a need for a deep penetration bomb, but coalition forces had none. So, they came up with idea to develop bunker buster bombs using old 8-inch (203 mm) artillery barrels as casings. These bombs weighed over 2 tons and carried 647 lb (293 kg) of high explosives. Additionally, laser-guidance was added to them and the bombs were designated "Guided Bomb Unit-28 (GBU-28)". Even Russians developed its own bunker buster, the KAB-1500L-Pr delivered via Su-24M and Su-34 aircrafts. The bomb weighs 1,500 kg (3,300 lb), with 1,100 kg (2,400 lb) high explosive penetrating warhead. It is laser guided and has a reported strike accuracy of 7 m (23 ft) CEP. It is capable of penetrating 10–20 m of earth or 2 m of reinforced concrete. The US has since then developed variety of custom-made bombs like Paveway series of laser-guided bombs and more.

Depth of Penetration reinforced concrete	Weapon Systems
1.8 metres (5 ft 11 in)	BLU-109 Penetrator	GBU-10, GBU-15, GBU-24, GBU-27, AGM-130, GBU-31(V)3/B & GBU-31(V)4/B
3.4 metres (11 ft)	BLU-116 Advanced Unitary Penetrator (AUP)	GBU-15, GBU-24, GBU-27, AGM-130
	BLU-118/B Thermobaric weapon	GBU-15, GBU-24, AGM-130
more than 6 metres (20 ft)	BLU-113 Super Penetrator	GBU-28, GBU-37
18 metres (59 ft)	BLU-127 Massive Ordnance Penetrator	GBU-57

 

Modern bunker busters use a conventional fuze, but some also include a microphone and microcontroller. The microphone listens, and microcontroller counts the number of floors until the bomb breaks through desired numbers of floors. Northrop Grumman is working on Hard Target Void Sensing Fuze (HTVSF), an electronic and cockpit programmable fuze capable of destroying deeply buried targets. It provides multiple delay arming and detonation times, as well as a void-sensing capability, which allows for precision activation of the fuze for 2,000-and-5,000-pound (910 and 2,270 kg) weapons to explode when they reach an open space in a deeply buried bunker. The traditional fuze on other hand is the same as a classic armor-piercing bomb; a combination of timer and a sturdy dynamic propeller on the rear of the bomb. The fuze is armed when the bomb is released, and detonates when the propeller stops turning and timer expires. Turkey is rumoured to be developing bunker busters, on the same lines such as the SARB-83 and NEB-84.

Other Types of Bunker Busters

Missiles

Bunker busters on missiles are not new thing. They are being developed and used since missiles came into existence, just that their accuracy and intensity has increased. The extra speed provided by a rocket motor allows for a greater penetration of a missile-mounted bunker buster warhead. To reach maximum penetration (i.e., impact depth), the warhead may only have a high-density projectile only. Such a warhead carries more energy than a warhead with chemical explosives (kinetic energy of a projectile at hypervelocity). India is reportedly developing a ‘bunker buster’ variant of the AGNI-5 missile with a compatible armour and concrete piercing warhead. Reports suggest India is also working on a bunker buster’ variant of the AGNI-3 missile. It may be known that both AGNI-3 and AGNI-5 missile are the most heaviest missiles in India’s arsenal and carry the heaviest warhead payload of 2.5 tons.

Nuclear

The nuclear bunker buster is the nuclear weapon version of the bunker buster. The non-nuclear component of the weapon is designed to enhance the penetration of the bomb into soil, rock, or concrete to deliver a nuclear warhead to a target. These weapons would be used to destroy deeply buried hardened, underground military bunkers. Theoretically radioactive nuclear fallout from such bombs will be reduced from that of a standard, air-burst nuclear device detonation because the bomb will have a relatively low explosive yield. However, since these bombs come into contact with large amounts of earth-based debris, they may, still generate significant fallout. Warhead yield and weapon design also have impact on the end result fall out of such bombs. An underground explosion may release a larger fraction of its energy into the ground, compared to an nuclear explosion at or above the surface which releases most of its energy into the atmosphere.

GBU-57 (MOP)

GBU-57 series MOP (Massive Ordnance Penetrator) is a 30,000-pound (14,000 kg) class, 20.5-foot-long (6.2 m) precision-guided munition "bunker buster" bomb. The "GBU" stand for "guided bomb unit" and has been developed by Boeing for the United States Air Force (USAF). It is composed of a BLU-127 bomb body and an integrated GPS/INS guidance package. There are 7 different types of GBU-57 bombs. Due to its massive size and weight, the GBU-57 MOP can only be carried by the Northrop B-2 Spirit strategic bomber, which can carry 2 of these. In future the B-21 Raider strategic bomber that is set to replace the B-2 Spirit strategic bomber will carry it.

The first test of GBU-57 were conducted with the Boeing B-52 Stratofortress. The first ever combat use of the GBU-57 MOP was on June 22, 2025, when six or seven Northrop B-2 Spirit stealth bombers dropped 12 or 14 GBU-57 bombs on Iran's Fordow Uranium Enrichment Plant and Natanz Nuclear Facility. The bomb is much larger than earlier USAF bunker-busters such as the 5,000-pound (2,300 kg) GBU-28 and GBU-37. In 2002, the US Air Force began the "Big BLU" (BLU = Bomb Live Unit) program to develop a series of very powerful conventional munitions. Two main weapons were associated with this concept: a blast variant, the GBU-43/B MOAB (Massive Ordnance Air Blast), a 21,700-pound conventional bomb designed to destroy a large area; and a penetrator variant, the GBU-57 MOP (Massive Ordnance Penetrator). The MOAB emerged in 2003, but the MOP project was paused for funding and technical difficulties.

Bomb damage assessment during the 2003 invasion of Iraq revealed that the US Air Force's bunker-busting bombs sometimes failed to destroy fortified military bunkers. This led to the resumption of the Big BLU project. In July 2004, the USAF asked defense contractors to develop a large, precision-guided bomb that could destroy targets deep underground, in caves, or in hardened bunkers. That year, the Defense Threat Reduction Agency (DTRA) and the Munitions Directorate of the Air Force Research Laboratory (AFRL) at Eglin Air Force Base launched the MOP project. GBU-57 MOP was designed by Boeing to be used with the B-2 Spirit. GBU-57 MOP was first tested in March 2007, in a DTRA tunnel at the White Sands Missile Range in New Mexico.

In July 2007, Northrop Grumman won a contract to refit the B-2, enabling it to carry two of the 14-ton GBU-57 MOP bombs. 2008 onwards, the MOP was tested under various conditions, including on rocket sleds at Holloman High Speed Test Track and from B-52 and B-2 strategic bomber aircraft at White Sands. US Congress approved the acceleration of the project in October 2009, but funding delays and changes in test-schedule delayed its deployment. The USAF finally started receiving the MOP in September 2011, and had received 16 MOPs by November 2011. In March 2012, there was an "operational stockpile" at Whiteman Air Force Base. By early 2013, the MOP had been integrated onto the B-2. By November 2015, 20 of the bombs were delivered for operational use to the USAF. In October 2019, the USAF awarded US$90 million contracts to 2 steel forging plants to make an unspecified number of case assemblies for the bomb's BLU-127C/B warhead.

Key Components of GBU-57

The GBU-57's explosive component is a bomb of the BLU-127 series, whose modular design accommodates improvements and upgrades. There are 7 different types of GBU-57 bombs. One variant of the BLU-127 bomb body contains 4,590 pounds (2,082 kg) of AFX-757 and 752 pounds (341 kg) of PBXN-114, a polymer-bonded explosive (PBX), for a total explosive payload of 5,342 pounds (2,423 kg). The PBX is optimized for controlled detonation in confined spaces. The bomb's casing is made from high-density Eglin steel alloy, engineered to survive the extreme stresses of deep penetration before detonation. The GBU-57 is a precision-guided munition integrated with GPS/INS guidance package which enables the bomb to strike targets with CEP of 2 meters of its target. Detonation timing is managed by the Large Penetrator Smart Fuse (LPSF), which adjusts the moment of explosion based on impact depth and the characteristics of the underground structure. In order to maintain trajectory and allow for mid-course adjustments, the GBU-57 has grid fins, not the planar fins found on most conventional bombs, because they can fold for storage in a B-2's bomb bays and offers greater control at high speeds. Grid fins have higher drag than planar fins, and so are usually smaller.

GBU-57 Combat Use

In June 2025, the 12-day war was fought between Iran Vs Israel/USA. USA joined the war on 11th day to conduct airstrikes on Iranian nuclear facilities. Whether the GBU-57 Massive Ordnance Penetrator (MOP) reliably destroyed Iran's deeply buried nuclear sites or not still a matter of discussion. Reportedly, the Fordow facility and the new halls under construction at Natanz are reported to be more than 80 meters underground, whereas the original Natanz enrichment plant was roughly only 20 m below the surface. The MOP reportedly able to penetrate about 18 m of reinforced concrete with a compressive strength of 5,000 psi. Reportedly Iran via domestic research has produced concrete exceeding 30,000 psi strength, which could sharply reduce any bomb's effective impact on any penetration depth.

GBU-57 dropped from B-2 Spirit strategic bombers was used by USAF to strike Iranian nuclear sites at Fordow, Natanz, and Esfahan on June 22, 2025. 7 Northrop B-2 Spirit stealth bombers dropped 12 MOPs on the Fordow Uranium Enrichment Plant and 2 MOPs on the Natanz Nuclear Facility. Only the B-2 Spirit is configured to carry the MOP; the B-21 Raider is slated to carry it. B-52 Stratofortress were used to test the MOP, but would requires special modification to drop one in combat.

Specifications and capabilities

Length: 20.5 feet (6.2 m)

Diameter: 31.5 inches (0.8 m)

BLU-127 bomb body weight: 27,125 pounds (12,304 kg)

Explosive weight: 5,342 pounds (2,423 kg)

AFX-757: 4,590 pounds (2,082 kg)

PBXN-114: 752 pounds (341 kg)

 

The GBU-57 MOP does not have a void-sensing fuze and detonates only after it comes to a stop, even if it has passed the target area. There is debate about the penetration capabilities of the bomb. The US Air Force says GBU-57s can penetrate up to 200 ft (60 m) of unspecified material before exploding. BBC reports that analysts at Janes Information Services, think GBU-57s can penetrate about 200 ft (60 m) of earth or 60 ft (18 m) of concrete. A separate source suggests GBU-57s penetration only up to 60 ft (18 m) into reinforced concrete with a compressive strength of 5,000 psi (34 MPa) and 8 ft (2.4 m) into 10,000 psi (69 MPa) reinforced concrete. So whether USAF strikes on Fordow, Natanz, and Esfahan on June 22, 2025 were stupendously successful will remain mystery unless Iran clarifies on it.