The U.S. military is exploring ways to expand the capabilities of one of its most widely used precision-guided munitions, with new plans focused on turning the 2,000-pound-class Joint Direct Attack Munition-Extended Range (JDAM-ER) into a more effective bunker-busting weapon capable of striking hardened and deeply buried targets from significantly greater distances.
The initiative, outlined in the Pentagon’s proposed Fiscal Year 2027 budget request, reflects growing concern over the increasing number of underground military facilities being developed by potential adversaries around the world. If successful, the effort could provide U.S. commanders with a more flexible and survivable option for attacking fortified structures while reducing risks to aircraft and crews.
The Defense Threat Reduction Agency (DTRA), the Pentagon organization responsible for countering weapons of mass destruction and developing technologies to defeat hardened targets, is leading the effort. Budget documents reveal that DTRA plans to evaluate existing hard-target defeat capabilities using the GBU-64 JDAM-ER and provide recommendations for future development aimed at enhancing penetration performance against hardened and deeply buried targets.
The project marks the latest chapter in the U.S. military’s long-running pursuit of more effective bunker-busting weapons. While the military already fields specialized penetrating munitions, officials appear interested in determining whether the relatively inexpensive and widely available JDAM-ER can be adapted to fill part of that mission set.
Unlike traditional bunker-buster bombs, which are often released relatively close to their targets, the JDAM-ER incorporates a wing kit that dramatically extends its range. The standard JDAM converts unguided bombs into GPS-guided precision weapons and can reach targets roughly 15 miles away under optimal conditions. By contrast, the JDAM-ER’s deployable wings allow it to glide as far as approximately 45 miles, depending on release altitude and flight profile.
That extended reach offers significant operational advantages.
Attacks on hardened facilities frequently require aircraft to fly near heavily defended targets protected by advanced air-defense systems. Such facilities are often among an adversary’s most valuable strategic assets, making them heavily guarded and difficult to approach safely.
By enabling aircraft to launch bunker-busting weapons from much farther away, a JDAM-ER-based penetrator could help reduce exposure to enemy defenses while maintaining strike effectiveness. This capability has become increasingly relevant as modern air-defense networks continue to improve in range, sophistication, and survivability.
The importance of stand-off strike capability has been highlighted repeatedly in recent conflicts, particularly during operations against Iranian nuclear and military infrastructure, where penetrating fortified facilities often required aircraft to approach dangerous airspace.
The GBU-64/B designation refers to the 2,000-pound-class JDAM-ER currently in U.S. military inventories.
Like other JDAM variants, the weapon is not a complete bomb in itself. Instead, it consists of a guidance and wing kit attached to existing unguided bomb bodies. The modular approach allows the military to transform a variety of conventional munitions into precision-guided weapons.
JDAM-ER kits are available for 500-pound, 1,000-pound, and 2,000-pound-class bombs. The currently confirmed operational version of the GBU-64, designated GBU-64(V)1/B, uses the Mk 64 Quickstrike air-dropped naval mine as its warhead.
However, Boeing, the system’s manufacturer, has previously stated that the JDAM-ER kit can be paired with the BLU-109/B penetrating bomb, a hardened steel-cased munition specifically designed for attacking bunkers and reinforced structures.
It remains unclear whether such a configuration is already fielded operationally within the U.S. military, but DTRA’s latest budget request suggests significant interest in evaluating precisely that kind of capability.
One of the central questions facing the program is whether the aerodynamic advantages of the JDAM-ER can be reconciled with the physical requirements of bunker-busting.
Penetrating weapons rely heavily on kinetic energy. A bomb striking at high speed and steep angles can punch through layers of concrete, rock, and soil before detonating. Traditional bunker-buster attacks therefore often involve weapons being dropped from high altitude and relatively close range to maximize impact energy.
The addition of wings creates aerodynamic drag that could potentially reduce terminal velocity and therefore penetration effectiveness.
Military planners may seek to overcome this limitation through flight-profile optimization. A JDAM-ER could glide toward a target from long range before transitioning into a steep terminal dive designed to maximize impact speed. Such an approach could preserve many of the weapon’s stand-off advantages while retaining enough kinetic energy for penetration missions.
Determining how effectively this balance can be achieved appears to be one of the key objectives of DTRA’s upcoming evaluation.
Beyond simply extending range, the JDAM-ER’s gliding capability opens up entirely new attack geometries that conventional bunker-buster bombs typically cannot achieve.
Traditional penetrating weapons usually strike from above at relatively steep angles. While effective against many hardened structures, this approach is not always optimal.
A gliding bunker-buster could approach a target from the side, enabling low-angle attacks against specific vulnerabilities. Such profiles may allow weapons to strike tunnel entrances, access shafts, ventilation systems, or exposed portions of underground facilities that are difficult to reach through vertical penetration alone.
Military analysts have long noted that many underground complexes remain dependent on a limited number of entry points and support infrastructure. Targeting these weak spots directly could significantly increase the effectiveness of a strike.
The ability to attack horizontally could also prove valuable against a broader range of targets, including dams, bridge supports, hardened command centers, and even ships docked in port. Heavy penetrating warheads have traditionally lacked the flexibility offered by cruise missiles in these scenarios, making the JDAM-ER concept particularly attractive from a weaponeering perspective.
Another intriguing element of DTRA’s budget request involves research into modernized skip-bombing techniques.
According to budget documents, the agency plans to conduct research and development aimed at creating new skip-bombing capabilities that could generate additional tactics and weaponeering options while enabling deeper access for penetrating weapons.
Skip bombing is a technique in which a bomb is released so that it bounces off the ground or water before continuing toward its target.
The tactic gained prominence during World War II. British forces famously employed specialized bouncing bombs during attacks on German dams, while U.S. aircraft in the Pacific frequently used skip bombing against Japanese shipping. The technique allowed bombs to strike vessels near the waterline, often producing devastating damage.
Applied to modern precision-guided munitions, skip bombing could potentially create entirely new methods for attacking underground facilities.
A weapon capable of skipping into tunnel entrances or other vulnerable openings before detonating could penetrate deeper into a target complex than conventional attack profiles permit. Such an approach might not destroy a facility outright, but it could severely complicate recovery efforts by collapsing access routes, damaging internal infrastructure, and trapping equipment underground.
Recent military operations against Iranian facilities have reinforced the strategic importance of defeating hardened and buried targets.
Over the past year, the United States and Israel have conducted strikes against a variety of Iranian nuclear and military sites, including facilities associated with uranium enrichment and missile development programs.
Operation Midnight Hammer in June 2025 brought renewed attention to the challenges involved in attacking deeply buried infrastructure. Although bunker-busting weapons were employed during those operations, questions have persisted regarding the extent of the damage inflicted on some underground facilities.
Subsequent imagery and intelligence assessments indicated that Iran continued efforts to restore access to certain sites. Iranian authorities reportedly took measures to reinforce tunnel entrances, cover ventilation shafts, and improve the survivability of underground complexes against future attacks.
These developments have highlighted a persistent challenge for military planners: even successful strikes may not completely eliminate hardened underground targets if critical access points remain recoverable.
Improved stand-off bunker-busters and advanced penetration tactics could provide additional options for addressing those concerns in future operations.
The Pentagon’s interest in enhancing bunker-busting capabilities extends far beyond Iran.
Military planners increasingly view underground infrastructure as a defining feature of modern strategic competition. Potential adversaries have invested heavily in subterranean facilities designed to protect critical assets from air and missile attack.
China has constructed extensive underground networks supporting missile forces, command-and-control facilities, air bases, and naval infrastructure. Russia maintains large numbers of hardened military installations, including command bunkers and strategic weapons facilities. North Korea is perhaps best known for its vast network of tunnels, underground bases, missile sites, and fortified artillery positions.
These facilities complicate military operations by increasing the number of weapons required to achieve desired effects and by reducing the effectiveness of conventional airpower.
As a result, the United States has launched several parallel efforts aimed at improving its ability to hold hardened targets at risk.
Among those initiatives are development of the Next Generation Penetrator, a future successor to the massive 30,000-pound GBU-57/B Massive Ordnance Penetrator, as well as a new nuclear bunker-busting weapon currently known as the Nuclear Deterrent System-Air-delivered.
The military has also recently fielded the GBU-72/B, a 5,000-pound-class conventional penetrator designed to bridge the capability gap between existing bunker-busters and the much larger Massive Ordnance Penetrator.
While larger and more powerful bunker-busters remain essential for defeating the most heavily fortified targets, a JDAM-ER-based penetrator could occupy an important niche within the broader strike arsenal.
The weapon would offer commanders a comparatively affordable, widely deployable, and long-range option for attacking a range of hardened structures without requiring specialized heavy bombers or massive munitions.
Future enhancements could become even more significant if paired with emerging technologies such as the jet-powered GBU-75/B JDAM-LR, a longer-range derivative currently in development.
For now, DTRA’s planned evaluations represent an early step in determining how far the concept can be taken. But as underground military infrastructure continues to proliferate around the world, the Pentagon’s interest in transforming the JDAM-ER into a versatile stand-off bunker-buster underscores a broader reality: the battle between hardened defenses and advanced penetration weapons is far from over.
