Joint Direct Attack Munition
The Joint Direct Attack Munition is a guidance kit that converts unguided bombs, or "dumb bombs", into all-weather precision-guided munitions. JDAM-equipped bombs are guided by an integrated inertial guidance system coupled to a Global Positioning System receiver, giving them a published range of up to. JDAM-equipped bombs range from. The JDAM's guidance system was jointly developed by the United States Air Force and United States Navy, hence the "joint" in JDAM. When installed on a bomb, the JDAM kit is given a GBU identifier, superseding the Mark 80 or BLU nomenclature of the bomb to which it is attached.
The JDAM is not a stand-alone weapon; rather it is a "bolt-on" guidance package that converts unguided gravity bombs into PGMs. The key components of the system are a tail section with aerodynamic control surfaces, a strake kit, and a combined inertial guidance system and GPS guidance control unit.
The JDAM was meant to improve upon laser-guided bomb and imaging infrared technology, which can be hindered by bad ground and weather conditions. Laser seekers are now being fitted to some JDAMs.
From 1998 to November 2016, Boeing completed more than 300,000 JDAM guidance kits. In 2017, it built more than 130 kits per day. As of January 2024, 550,000 kits had been produced.
History
Development
The U.S. Air Force's bombing campaign during the Persian Gulf War was less effective than initially reported, in part because it had no precision bombs that were accurate in all types of weather. Laser guidance packages on bombs proved exceptionally accurate in clear conditions, but amid airborne dust, smoke, fog, or cloud cover, they had difficulty maintaining "lock" on the laser designation; they also could not be released at high altitudes. Research, development, testing and evaluation of an "adverse weather precision guided munition" began in 1992. Several proposals were considered, including a radical concept that used GPS.At the time, there were few GPS satellites and the idea of using satellite navigation for real-time weapon guidance was untested and controversial. To identify the technical risk associated with an INS/GPS guided weapon, the Air Force created in early 1992 a rapid-response High Gear program called the "JDAM Operational Concept Demonstration" at Eglin Air Force Base. Honeywell, Interstate Electronics Corporation, Sverdrup Technology, and General Dynamics were hired to help the USAF 46th Test Wing demonstrate the feasibility of a GPS weapon within one year. The OCD program fitted a GBU-15 guided bomb with an INS/GPS guidance kit and on 10 February 1993, dropped the first INS/GPS weapon from an F-16 on a target downrange. Five more tests were run in various weather conditions, altitudes, and ranges. The OCD program demonstrated a Circular Error Probable.
Eager to arm the B-2 Spirit stealth bomber, which lacked a laser designator, with an interim precision guided conventional munition before the JDAM could be fielded, Northrop Grumman launched a program called "GPS Aided Munition", or GAM, which paired inertial navigation with GPS to correct for drift and allowed for exceptional accuracy while still retaining combat functionality in GPS-denied environments. The GAM munitions consisted primarily of 2,000 lb Mk 84 bombs with a tail guidance kit added, which were designated GBU-36/B GAM; these munitions are considered the direct predecessors of the JDAM. The GAM munitions were combined with a GPS Aided Targeting System on the B-2, which could interface with the AN/APQ-181 synthetic aperture radar to enable extreme accuracy with a 20-foot CEP, approximately half of what a JDAM without GATS/radar support could achieve. GAMs were always intended as an interim solution until the JDAM could replace them; with McDonnell Douglas already having been selected for the JDAM program in October 1995.
The first JDAM kits were delivered in 1997, with operational testing conducted in 1998 and 1999. During testing, over 450 JDAMs were dropped achieving a system reliability in excess of 95% with a published accuracy under CEP. In addition to controlled parameter drops, the testing and evaluation of the JDAM also included "operationally representative tests" consisting of drops through clouds, rain and snow with no decrease in accuracy from clear-weather tests. In addition, there have been tests involving multiple weapon drops with each weapon being individually targeted.
JDAM and the B-2 Spirit stealth bomber made their combat debuts during Operation Allied Force. The B-2s, flying 30-hour, nonstop, round-trip flights from Whiteman Air Force Base, Missouri, delivered more than 650 JDAMs during Allied Force. As this utilized most of the US GBU-31 inventory, which only numbered 600 at the start of the conflict, this was supplemented by an additional 224 GAMs. An article published in the Acquisition Review Journal in 2002 cites that "during Operation Allied Force... B-2s launched 651 JDAMs with 96% reliability and hit 87% of intended targets..." Due to the operational success of the original JDAM, the program expanded to the Mark 82 and Mark 83, beginning development in late 1999. As a result of lessons from Operation Enduring Freedom and Operation Iraqi Freedom, both the US Navy and US Air Force pursued improvements to the kits such as better GPS accuracy as well as a laser seeker for terminal guidance for use against moving targets.
JDAM bombs are inexpensive compared to alternatives such as cruise missiles. The original cost estimate was $40,000 each for the tail kits; however, after competitive bidding, contracts were signed with McDonnell Douglas for delivery at $18,000 each. Unit costs, in current-year dollars, have since increased to $21,000 in 2004 and $27,000 by 2011. To the cost of the tail kit should be added the costs of the Mk80-series iron bomb, the fuse and proximity sensor which bring the overall weapon cost to about $30,000. For comparison, the newest Tomahawk cruise missile, dubbed the Tactical Tomahawk, costs nearly $1.87 million.
Operational use
Guidance is facilitated through a tail control system and a GPS-aided inertial navigation system. The navigation system is initialized by transfer alignment from the aircraft that provides position and velocity vectors from the aircraft systems. Once released from the aircraft, the JDAM autonomously navigates to the designated target coordinates. Target coordinates can be loaded into the aircraft before takeoff, manually altered by the aircrew in flight prior to weapon release, or entered by a datalink from onboard targeting equipment, such as the LITENING II or "Sniper" targeting pods. In its most accurate mode, the JDAM system will provide a minimum weapon accuracy CEP of or less when a GPS signal is available. If the GPS signal is jammed or lost, the JDAM can still achieve a CEP or less for free flight times up to 100 seconds.The introduction of GPS guidance to weapons brought several improvements to air-to-ground warfare. The first is a real all-weather capability since GPS is not affected by rain, clouds, fog, smoke, or artificial obscurants. Previous precision guided weapons relied on seekers using infrared, visual light, or a reflected laser spot to "see" the ground target. These seekers were not effective when the target was obscured by fog and low altitude clouds and rain, or by dust and smoke.
The second advantage is an expanded launch acceptance region. The LAR defines the region that the aircraft must be within to launch the weapon and hit the target. Non-GPS based precision guided weapons using seekers to guide to the target have significant restrictions on the launch envelope due to the seeker field of view. Some of these systems must be launched so that the target remains in the seeker field of view throughout the weapon trajectory. This requires the aircraft to fly generally straight at the target when launching the weapon.
This restriction is eased in some other systems, such as the GBU-15 and the AGM-130, through the ability of a Weapon System Operator in the aircraft to manually steer the weapon to the target. Using a WSO requires a data link between the weapon and the controlling aircraft and requires the controlling aircraft to remain in the area as long as the weapon is under manual control. Since GPS-based flight control systems know the weapon's current location and the target location, these weapons can autonomously adjust the trajectory to hit the target. This allows the launch aircraft to release the weapon at very large off-axis angles including releasing weapons to attack targets behind the aircraft.
The third advantage is a true "fire-and-forget" capability in which the weapon does not require any support after being launched. This allows the launching aircraft to leave the target area and proceed to its next mission immediately after launching the GPS guided weapon.
Another important capability provided by GPS-based guidance is the ability to completely tailor a flight trajectory to meet criteria other than simply hitting a target. Weapon trajectories can be controlled so that a target can be impacted at precise headings and vertical angles. This provides the ability to impact perpendicular to a target surface and minimize the angle of attack, detonate the warhead at the optimum angle to maximize the warhead effectiveness, or have the weapon fly into the target area from a different heading than the launch aircraft. GPS also provides an accurate time source common to all systems; this allows multiple weapons to loiter and impact targets at preplanned times and intervals.
In recognition of these advantages, most weapons including the Paveway, GBU-15, and the AGM-130 have been upgraded with a GPS capability. This enhancement combines the flexibility of GPS with the superior accuracy of seeker guidance.
Despite their precision, JDAM employment has risks. On 5 December 2001, a JDAM dropped by a B-52 in Afghanistan nearly killed Hamid Karzai while he was leading anti-Taliban forces near Sayd Alim Kalay alongside a US Army Special Forces team. A large force of Taliban soldiers had engaged the combined force of Karzai's men and their American SF counterparts, nearly overwhelming them. The SF commander requested Close Air Support to strike the Taliban positions in an effort to stop their advance. A JDAM was subsequently dropped, but instead of striking the Taliban positions, it struck the Afghan/American position, killing three and injuring 20. An investigation of the incident determined that the U.S. Air Force Tactical Control Party attached to the Special Forces team had changed the battery in the GPS receiver at some point during the battle, thereby causing the device to return to "default" and "display its own coordinates." Not realizing that this had occurred, the TACP relayed his own coordinates to the delivery aircraft.
On 5 May 2023, during the 2022 Russian invasion of Ukraine, MSN reported that Russia was able to jam the GPS guidance system to cause JDAMs to miss their targets. The leaked Pentagon document described the JDAMs as being particularly susceptible to the disruption.
On 6 June 2023, the Royal United Services Institute released a commentary by an electronic warfare expert on the jamming of JDAMs by Russian forces. The paper notes that the Russian R-330Zh Zhitel has had impacted GPS signals that JDAMs rely on. GPS signals are "very weak by the time they have travelled the 10,900 nautical miles from the satellite to Earth", making them "easy to jam with comparatively little power". In the "early 2000s" the US military rolled out the Selective availability anti-spoofing module, along with encrypted military M-code GPS signaling to ensure that the JDAM only accepts signals with correct encryption and rejects all other signals. However, according to one electronic warfare expert who spoke to RUSI, despite the mentioned steps to increase jamming resiliency, the "sheer brute force" of a powerful jamming signal can prevent the JDAM's global navigation satellite system receiver from obtaining the encrypted signal.
Counter-EW systems, while classified, might allow a JDAM to recognize a jamming signal and its direction and "block out" signals coming from that direction. A GNSS receiver will "typically need to 'see' – that is have an uninterrupted Line-of-Sight with – at least four satellites", and will "often" have more satellites available to it. Thus, blocking signals from one direction might not affect the receiver's ability to "see" other satellites. Russian forces may choose to respond by placing more jammers in order to deny a line of sight to the satellites that it requires. Russian EW units might also have the ability to spoof or fake the M-Code that it confuses the JDAM as to its location and time. Ukrainian forces have been able to locate Russian jammers and hit them with "kinetic" attacks such as artillery. Several Russian EW units have been targeted and lost equipment.
On 13 August 2024, Ukrainian Su-27 launched a JDAM at a Russian command post in Tetkino, which was reportedly destroyed.
In December 2023, the WSJ report stated that US arms shipments to Israel since the start of the Gaza war included approximately 3,000 JDAMs. Israeli F-15I fighter jets are believed to have used BLU-109 bunker buster bombs with JDAM guidance kits in the strikes that killed Hezbollah leader Hassan Nasrallah in Beirut, Lebanon on 27 September 2024.