Joint Direct Attack Munition

The Joint Direct Attack Munition, usually abbreviated to JDAM, is an add-on guidance kit that converts a conventional Mark 8x series conventional bomb into a precision-guided munition of relatively low cost. In the 2003 Iraq War, the majority of bombs dropped by the U.S. were JDAMs. Pure unguided gravity bombs are used less and less.

One of the classic principles of war is mass. Originally, this meant the number of soldiers that could be used in attacking a single point. Later on, it referred to the weight of artillery shells that could be delivered to that target. Precision-guided munitions, however, introduce a new way of regarding mass: many soldiers or shells are not needed, if an adequately destructive munition can be delivered to the exact place where it will do the most damage. Precision is a force multiplier.

Admiral James O. Ellis, former commander, U.S. Strategic Command, said "We've migrated the number of sorties it will take to hit a target to the number of targets that one sortie can strike.

The JDAM components, made by Boeing, convert unguided (so-called "dumb") bombs into guided ("smart") bombs whose preliminary drop and target coordinates are set immediately before they are dropped from the aircraft. This is an example of the go-onto-location-in-space paradigm. Initially the guidance system was used only inertial but newer models also use GPS and laser guidance. In later versions, a go-onto-target capability, adding terminal guidance, is optional.

While troops on the ground could not, at first, directly control a JDAM, they can use a GPS-equipped laser rangefinder to take a precise sighting on the target and radio the data to the bomber. A new laser-guided version, the GPU-54, replaces GPS with a laser seeker, and can home on a target, including a moving target, marked with a ground-based laser designator rather than a rangefinder, considerably increasing precision in good weather, when the ground personnel can see the target. Since the laser signals are encoded and each JDAM is told which code to follow, several JDAMs at a time can be released from a single aircraft. The designation signals can come from different aircraft or ground observers.

Yet another approach uses imaging radar to determine the target coordinates to be loaded into the bomb. This appears to be one of the functions of the AN/APS-149 Littoral Surveillance Radar System on the P-3 Orion and P-8 Poseidon maritime and overland surveillance aircraft.

Uses and economics
In Fiscal Year 2010, a typical JDAM kit cost approximately $30,000 exclusive of reusable aircraft equipment and the bomb itself, with expected price reductions into the $25,000 range. A high probability of destroying one target with one bomb, as well as other operational advantages, indicate it saves money in comparison to traditional bombs.

Initial coordination
By the Gulf War, accuracy from medium altitude improved somewhat, but the inherent inaccuracies of "dumb" munitions obviated the "smarter" delivery platform. Dumb bombs had reached their limit of utility against point targets. No matter how accurate the release, for example, an unguided bomb, once released, could not compensate for sudden winds over the target. The PGMs available there used laser and television guidance, which had operational limitations, especially in the weather and land characteristics in Saudi Arbia and Iraq.

At first, JDAMs were used purely against targets predetermined by air planners, but there was an increasing need, critical in the Afghanistan War (2001-), to be directly responsive to the needs of forward air controller personnel with ground troops, to provide close air support. It had long been assumed that close air support needed direct target marking by a ground or air observer, typically with a laser. Another approach was to specify the target in relation to a beacon. Groiund personnel, had had the capability to use laser designators for the GOT model, but that required they stay in line of sight of the target, possibly exposing themselves.

Another model, more precise than the smoke grenade, was to place a radio or radar offset beacon near the target, but the troops still face the problem of precise angular and distance measurement from the beacon to the target. In the Afghanistan campaign of 2001, a new technique was adopted, only recently believed possible: ground-aided precision strike (GAPS). To put GAPS in practice, MG Daniel Leaf, USAF Director of Operational Requirements for Air and Space Operations said, in 2002, "If you had offered the B-1 with JDAMs in direct support of ground forces as a solution 10 years ago, I would have laughed heartily because it’s not what we envisioned." The JDAM's principal guidance mechanism is inertial, with a GPS correction option: a GOLIS model.

"'CAS and GAPS operations do not care what color of airpower is delivering the weapons. Certain segments of the USAF wanted to break out the use of heavy bombers and term it “bomber CAS. However, at the joint CAS symposium held at Eglin, the Navy and Marine Corps were successful in not letting the Air Force call this by a different name."

"'If heavy bombers are supporting ground troops in the traditional CAS role, then a name change for that aspect is not needed. [What is being discussed, however, is a new mission:] 'Precision firepower called in by TACPs on the ground [is] GAPS and [needs its own doctrine]. The situation in Afghanistan was unique; there was not a large-standing opposing army that was conducting maneuvers to bring firepower to bear against our forces... Airpower was the maneuvering element that was supported by the small fire support teams on the ground. The small ground units have been instrumental in calling in the precise air strikes [especially when Army Special Forces were augmented with Air Force combat controllers]. This emerging mission goes beyond the joint definition of CAS."

General Chuck Horner, the joint air commander during Operation DESERT STORM, likened it to giving infantrymen a "2000 pound hand grenade" (i.e., a 2000 pound JDAM guided bomb) from a long-range bomber loitering overhead.

In the Air Force GAPS doctrine, ground forces were augmented with Air Force combat controllers, equipped with the  Viper, which combined off-the-shelf Leica GeoSystems Viper laser range finder binoculars, with integral compass and inclinometer but no GPS,  to triangulate targets in Afghanistan. The Viper is capable of a lasing distance from 25 meters to 4,000 meters. The unit runs off of a commercial camera battery. The Special Forces operator radioed their own location, as determined by a separate GPS, and gave Viper-derived coordinates relative to that position, to the bomber.

Voice communication did not provide full situation awareness for all forces involved. The Viper system, however, allowed communications between one team and only one aircraft. More advanced systems allow network-centric warfare that can send the optimal aircraft to the target, using linkages with the Joint Tactical Information Distribution System (JTIDS), especially the Link-16 variant that can send information to fighters and Army Enhanced Position Location Reporting System (EPLRS) terminals.

Improvements
An improved version is the the Long-Range Advanced Scout Surveillance System (LRAS3) for general surveillance, as well as detecting and designating targets. This device is routinely provided to Reconnaissance, Surveillance and Target Acquisition Squadrons of Brigade Combat Teams, as well as to special reconnaissance personnel. The LRAS3 gives 24-hour capability with the combination of:
 * Forward-looking infrared (FLIR) sensor
 * Global Positioning System
 * eyesafe laser rangefinder
 * Day TV (DTV) camera.

Where tactical situations permit, the ground troops can use a laser designator to provide terminal guidance to the later bombs, such as the GBU-51, which can home on a laser spot after midcourse guidance by GPS/INS. This also allows moving targets to be hit.

Operational experience
JDAM smart bombs have been used in Operation Allied Force in 1999; Operations Southern Watch and Enduring Freedom; and in the Gulf War.

The early Afghanistan attempts, without a data link to the bomber, still required voice coordination to give the bomber the coordinates . This led to one "friendly fire" incident killed three United States Army Special Forces soldiers and wounded 19 others. A controller had been using a hand-held GPS receiver, whose battery failed. On replacing the battery, the unit reinitialized to show the controller's own position, not the offset from it he had been targeting. He passed the coordinates to a B-52 crew, who had no way of knowing it was the wrong position. They entered it as given, and the JDAM flew accurately and unfortunately onto its own controller's position. .

This incident, in the early phase of Afghanistan operations, involved a joint Afghan-U.S. team including Hamid Karzai, the current President of Afghanistan.

Design
A basic JDAM has several subsystems:
 * Tail control subsystem, which contains the guidance electronics, the movable fins that actually steer the bomb, and the actuators that move the fins
 * Strakes, or metal aerodynamic surfaces that give lift and stability, usually attached to the midsection of the bomb casing but sometimes to the nose
 * Hardback, containing the shackles that hold the bomb to the carrying aircraft, as well as MIL-STD-1760 and MIL-STD-1553 electrical/electronic interfaces

Specifications
There are a large number of JDAM designations, not all in service. The main model number (e.g., GBU-31 for a 2000 pound weapon) designates the bomb weight supported by the JDAM kit. Additional suffixes identify using service (Air Force or Navy), and versions of the guidance kit. The JDAM guidance kits, designated in the KMU-55x series, attach to bombs including the 2000 lb BLU-109 hard-target-penetrator, the 2000-pound MK 84/BLU-117, the 1,000-pound MK 83/BLU-110, the Air Force'sGBU-39 Small Diameter Bomb or the 500-pound MK 82/BLU-111 bombs.

While the Navy and Air Force versions are ballistically identical, the Navy versions usually have a wrinkled gray heat-resistant paint and internally use insensitive high explosive, while the Air Force versions have been painted green. For generality, the Navy variant is becoming the standard.

500 pound class
GBU-38(V)/B is the designation for 500 lb class JDAM bombs with guidance kits from Boeing. At least two different types of warhead can be used with the 500 lb JDAM tailkits:


 * MK 82: Standard 500 lb LDGP (Low-Drag General Purpose) bomb
 * BLU-111/B: Instead of the MK 82, the BLU-111/B warhead can also be used in the GBU-38/B series JDAMs. The BLU-111/B is externally identical to the MK 82, but uses the PBXN-109 thermally insensitive explosive. The BLU-111A/B variant, used by the Navy, has external protective coating. ''The extgernal protective coating is gray, rather than Air Force green."
 * BLU-126/B: The BLU-126/B LCDB (Low Collateral Damage Bomb) is externally identical to the BLU-111/B, but is filled with less explosives for a reduced fragmentation pattern blast radius. The LCDB was developed by the U.S. Navy for use in situations where friendly forces and/or civilians are close to the target. Even further reducing collateral damage are pure kinetic versions filled with concrete.

1000 pound class
Current production JDAMs with 1000 lb class warheads are designated in the GBU-32(V)/B (and formerly also GBU-35(V)/B) series. At least two different types of warhead can be used with the 1000 lb JDAM tailkits:
 * MK 83: Standard 1000 lb LDGP (Low-Drag General Purpose) bomb
 * BLU-110/B: Instead of the MK 83, the Navy can also use the BLU-110/B warhead in their GBU-32(V)2/B series JDAMs. The BLU-110/B is externally identical to the MK 83, but uses the PBXN-109 thermally insensitive explosive. The BLU-110A/B and -110B/B variants, which are the ones that are actually used by the Navy (indicated by "BLU-110/B" in the table below), have external protective coating.

2000 pound class
GBU-31 series designations use 2000 pound bombs.


 * MK 84: Air Force standard 2000 lb LDGP (Low-Drag General Purpose) bomb
 * BLU-109/B: 2000 lb class penetrator warhead
 * BLU-117/B: Instead of the MK 84, the Navy can also use the BLU-117/B warhead in their GBU-31(V)2/B series JDAMs. The BLU-117/B is externally identical to the MK 84, but uses the PBXN-109 thermally insensitive explosive.
 * BLU-119/B: Crash PAD (Prompt Agent Defeat) weapon, a blast/fragmentation warhead to damage fixed biological/chemical targets without contaminating the area; external shape identical to MK 84


 * Length: Length: (JDAM and warhead)
 * GBU-31 (v) 4/B: 148.6 inches (377.4 centimeters)
 * GBU-32 (v) 2/B: 119.5 inches (303.5 centimeters)**; GBU-38/B: 92.64 inches. Wingspan: GBU-31: 25 inches (63.5 centimeters); GBU-32: 19.6 ins. (49.8 centimeters). Weight: (JDAM and warhead) GBU-31 (v) 2/B: 2,036 pounds (925.4 kilograms); GBU-31 (v) 4/B: 2,115 pounds (961.4 kilograms); GBU-32 (v) 2/B: 1,013 pounds (460.5 kilograms); GBU-38/B: 590 pounds.
 * GBU-32 (v) 2/B: 119.5 inches (303.5 centimeters)**; GBU-38/B: 92.64 inches. Wingspan: GBU-31: 25 inches (63.5 centimeters); GBU-32: 19.6 ins. (49.8 centimeters). Weight: (JDAM and warhead) GBU-31 (v) 2/B: 2,036 pounds (925.4 kilograms); GBU-31 (v) 4/B: 2,115 pounds (961.4 kilograms); GBU-32 (v) 2/B: 1,013 pounds (460.5 kilograms); GBU-38/B: 590 pounds.

Ceiling: 45,000-plus feet (13,677 meters). Ceiling is the highest altitude the weapon can be released from and to be expected to perform its mission. The JDAM has a range of up to 15 miles (24 kilometers).

Derivatives
There is a trend to make the bombs both more accurate, but, sometimes counterintuitively, to have smaller areas of effect.

GPS supplement to intertial guidance
Once dropped, the JDAM navigates to the target without human input. In its most accurate mode, when GPS data is available, the JDAM system will have an error of less than 13 meters (about 40 feet). Since it does not rely on external commands, it cannot be jammed -- the worst case would be that jamming GPS would reduce its accuracy to that of the inertial-only guidance, 30 meters.

Longshot JDAM torpedo
Another application, called Longshot, combines JDAM guidance with torpedoes. The combination, called Longshot, would allow high-altitude drops both from the P-8 Poseidon and the older P-3 Orion.

Terminal guidance
Both for increased accuracy and to deal with moving targets, a prototype terminal guidance seeker was evaluated in 1997-1998. Called DAMASK (Direct Attack Munitions Affordable Seeker), it used IIR (Imaging Infrared) seeker and associated control algorithms to improve CEP to 3m (10 ft).

Terminal guidance, however, was abandoned until 2006, with a competition, by the Air Force and Navy, for a Dual Mode Guided Bomb (DMGB) program, which was won by Boeing's LJDAM that  Precision Laser Guidance Set (PLGS) to JDAM guided bombs. The other two contenders were Lockheed Martin's DMGB and Raytheon's Enhanced Paveway II (EGBU). Inertial and GPS guidance still gets the JDAM to the target area, but it then follows a laser designator spot onto a potentially moving target.

Called the GBU-54, it has been tested on F-16 Fighting Falcon and now B-52 aircraft, and began used operationally in Iraq in 2008.

Future
A recent demonstration showed the power of preprogrammed targeting for the JDAM: a B-2 Spirit stealth heavy bomber released 80 JDAMs in 2 seconds, each aimed at a different target up to 15 miles away.

The higher and faster that a basic guided bomb can be dropped, the farther the dropping aircraft can be from the target -- and safer from its defenses. This is one of the reasons that the attack version of the F-22 Raptor can drop from at least 50,000 feet and at supersonic speed, which gives it a much greater JDAM range than a current fighter-bomber or heavy bomber.