Indian Defence

How Do Bunker Busters Work?

Bunker busters are specialized penetrating and explosive munitions which are designed to destroy fortified targets such as bunkers, underground facilities and heavily reinforced structures. The concept of penetrating fortified targets dates back to ancient warfare, with early attempts using primitive siege weapons and rudimentary explosives. However, it wasn’t until the 20th century, particularly during World War II and the Cold War era, that significant advancements were made in developing dedicated bunker buster munitions. The need to penetrate heavily fortified Nazi bunkers during the European theatre of World War II prompted the development of specialized bombs, laying the groundwork for future innovations in this field. In today’s warfare, these munitions are one of the turning point inventions which have had a severe impact in fighting terror groups among various other applications.

Coming Into Existence

During the Gulf War of 1991, the coalition forces were aware of numerous subterranean military bunkers in Iraq that were so heavily fortified and deeply entrenched that conventional munitions were ineffective against them. In response, the U.S. Air Force initiated an extensive research and development endeavor aimed at devising a novel bunker-busting bomb capable of reaching and neutralizing these underground targets. In a remarkably short span of time, a prototype was devised. The new bomb boasted several distinctive features. Its outer casing comprised a robust approximately 16-foot (5-meter) segment of artillery barrel measuring 14.5 inches (37 cm) in diameter. Artillery barrels are constructed from exceptionally durable hardened steel to withstand the rigors of repeated artillery shell detonations upon firing. Internally, the bomb housed nearly 650 pounds (295 kg) of tritonal explosive. Tritonal, a blend of TNT (80 percent) and aluminium powder (20 percent), was chosen for its enhanced brisance, or the speed at which the explosive reaches its maximum pressure. The inclusion of aluminium renders tritonal approximately 18 percent more potent than pure TNT. Positioned at the front of the barrel was a laser-guidance mechanism. This system allowed for precise targeting, with a ground-based spotter or an aircraft illuminating the designated target with a laser, enabling the bomb to home in on the illuminated spot. The guidance assembly manipulated the bomb’s trajectory through the inclusion of fins as integral components. The bomb also featured stationary fins affixed to the end of the barrel to ensure stability during flight. Upon completion, the bomb, referred to as the GBU-28 or BLU-113, measured 19 feet (5.8 meters) in length, 14.5 inches (36.8 cm) in diameter, and weighed approximately 4,400 pounds (1,996 kg).

F-15 Eagle dropping a GBU-28

Types of Bunker Busters operational today

Guided Bomb Units – Guided bomb units are precision-guided munitions equipped with guidance systems to accurately strike targets. They come in various sizes and configurations, with bunker buster variants designed specifically to penetrate hardened targets. These munitions typically feature advanced guidance systems such as laser, GPS, or inertial navigation, allowing for precise targeting and engagement of underground or fortified structures. Bunker buster GBUs often employ powerful explosives and specialized casing materials to ensure deep penetration into the target before detonation.

Missiles-type BBs – Missiles play a significant role in bunker busting due to their long-range capability and precision guidance systems. Modern bunker buster missiles, such as the AGM-158 Joint Air-to-Surface Standoff Missile (JASSM), are designed to deliver penetrating warheads to deeply buried or heavily fortified targets. These missiles may utilize advanced seeker technologies, including infrared, radar, or GPS guidance, to accurately navigate and strike underground facilities or bunkers.

Standoff Weapons – Standoff weapons refer to munitions that can be launched from a distance, allowing aircraft or other platforms to remain outside the range of enemy defenses. Bunker buster variants of standoff weapons, such as the AGM-154 Joint Standoff Weapon (JSOW), are equipped with specialized warheads designed to penetrate hardened targets. These weapons may employ various guidance systems, including inertial navigation or satellite guidance, to accurately deliver their payloads to underground or fortified structures.

Cluster Munitions – Cluster munitions are air-dropped or ground-launched weapons that dispense multiple submunitions over a wide area. Bunker buster cluster munitions, like the Sensor-Fuzed Weapon (SFW), may contain submunitions equipped with sensors to detect and engage hardened targets. These munitions are designed to saturate the target area with explosives, increasing the likelihood of penetrating underground bunkers or fortified facilities.

Nuclear BBs – The nuclear bunker buster serves as the nuclear-equipped version of the traditional bunker buster munition. Its non-nuclear component is specifically engineered to enhance penetration through soil, rock, or concrete, facilitating the delivery of a nuclear warhead to its intended target, typically deeply buried underground military bunkers. The aim is to destroy fortified structures with reduced radioactive fallout compared to standard air-burst nuclear detonations due to their lower explosive yield. Some of these are operational while some are under development to incorporate better and more advanced features, and have become a part of Tactical Nuclear Weapons.

Testing of Israel’s MPR-500 (penetrating though four layers of double-reinforced concrete walls)

How do BBs work?

The primary priority of bunker busters is to penetrate several meters of reinforced concrete or go deep into the ground and hit the underneath desired target without having a premature explosion on the first contact. From the open source information available and generic constituents used in these developments, BBs basically have a mixture of 80% TNT and 20% aluminium powder, called Tritonal. This was the first used successful case which has later given birth to different types of warhead constituents for different types and applications. The aluminium increases the crushing effect of the TNT and is said to be 18% more powerful than using a full percent of TNT only. Laser homing guidance is used for controlling the direction and fins are present for stability and guiding the bomb to the exact position. All of these is packed in a rigid tube of hardened steel and is air-dropped. Bunker busters are heavy-grade weapons and the kinetic energy and speed gathered due to gravity once in freefall enhances the penetrating power further. Unlike missiles which fly horizontally or unguided vertically dropped conventional bombs, BBs engage in nose-diving with the tip of the bomb having contact first. Upon hitting the ground it impales straight through the surface with its nose after which comes the final part. A delay mechanism is needed so that the bomb doesn’t prematurely explode on touching ground first even before reaching the target. This is done by using a Delay fuze or Hard Target Smart Fuze mechanisms. Properly developed bunker busters can penetrate 100ft into the ground and 20ft of solid concrete even after dropped from 20000 ft. More advancements are being made to make them heavier to give them more kinetic energy once it hits the target or smaller in diameter which gives more penetration into the target. In addition to these, rocket boosters are being installed in many to give added speed once deployed from the fighter-bombers or dedicated bomber aircrafts.

GBU 57A/B Massive Ordnance Penetrator (MOP): The Most Powerful Bunker Buster till now

Initially being developed by Northrop Grumman and Lockheed Martin and further handed over to Boeing for manufacturing, the GBU-57A/B is a nightmare for the enemy. It is a precision guided 3000o-pound (14000kg) bunker buster used only by the United States Air Force. It stands at 6.2m length and 0.8m diameter and carries a 5342-pound warhead with a high-explosive mixture yield of TNT, the constituents of which remain classified. It uses a GPS-guided inertial navigation system – the same guiding mechanism which is used in several modern cruise missiles. The MOP can reportedly penetrate upto 200ft (61m) of concrete. Nothing much of this weapon is in the hands of the public. The only aircraft which can successfully carry this is the B-2 Spirit stealth bomber, which can carry two of these, although tests are being done to be carried by the B-52 Stratofortress and inconsideration for the upcoming B-21 Raider stealth bomber.

GBU-57 (Image Credits –

Also Read, Explained: How Explosive Reactive Armour Works?

India’s Bunker Busters

India doesn’t have a dedicated line of bunker buster munitions but fields some of the BB variants of conventional bombs.

SPICE 2000 – Being the most prominent example for India, this weapon was used in hitting the terror camps in the Balakot Air Strikes. The bunker busting variant itself was used in those February 2019 air strikes which was followed by an additional order of these bombs in August 2019. Designed by Rafael Advanced Defence Systems, Spice 2000 uses a GPS-integrated Inertial Navigated System and offers a stand off range of 60 – 100km. It features a high accuracy of less than 3m CEP (Circular Probable Error). India uses the Mk84 warhead in the Spice 2000s – the same 2000 pound warheads and the largest of them used in US’ Mark 80 handling General Purpose Bombs. India’s Mirage 2000 and Sukhoi Su-30 MKIs are the only aircrafts to be able to carry this weapon but near future will see the Tejas Mk2 as an addition.

HAMMER – Developed by Safran Electronics and Defense, the HAMMER is a French air-to-ground weapon system which although isn’t a dedicated bunker buster, has redeemable characteristics for the BB variant. It offers multiple guidance options including GPS-INS system, laser guidance and infrared imaging, enabling precise targeting in various operational scenarios. It has a 20 – 70km standoff range and a CEP of less than 10m. The bunker busting HAMMER variant is an all-weather weapon and can function equally effective in day-night-adverse weather conditions due to the flexible guidance options. HAMMER comes with options for multiple weights of warheads – 125 kg, 250 kg, 500 kg and 1000 kg. Currently India’s Rafales and Tejas are the only aircrafts capable of carrying HAMMERs. The Rafale can carry upto 3 HAMMER 1000s while the Tejas can carry 5 HAMMERs as a compromising move for other weapons on its hardpoints.

HAMMER AASM of Safran displayed at the HAL Pavilion, DSA 2022 (Image Credits –

Subhodip Das

An Average Mechanical Engineering student from Jadavpur University, Kolkata who dreams of having a fully customized AR-15 draped on the wall....very childish ain't it ! Well apart from that, Art is the one absolute thing I practically live for.

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