Lon Nordeen examines the Joint Direct Attack Munition (JDAM), one of the most significant new weapons to enter the US military arsenal in recent years.
EFFECTIVE ATTACK missions against targets in Kosovo, which NATO pilots have been flying since March 24, 1999, have been a challenge due to the rules of engagement pilots and commander have had to follow. They have also been complicated because of poor weather. The newly-fielded Joint Direct Attack Munition (JDAM) dropped from the B-2A Spirit stealth bomber has allowed NATO forces to hit targets when poor weather hampered the effective employment of laser-designated or TV/Imaging Infra-red (MR) guided bombs and missiles.
One of the primary lessons of the Gulf Conflict and subsequent operations over Iraq, Bosnia and the ongoing Kosovo fighting, is that air attacks from medium altitude using precision guided munitions (PGMs) are the best mode of improving survivability and increasing target coverage with a smaller, post-Cold War, air inventory. The use of PGMs places fewer aircraft and aircrew at risk to enemy defences, hits targets with a much reduced number of sorties, and allows for a smaller force. In addition, PGMs reduce the risk of collateral damage, non-combatant casualties, and (usually), minimise the negative political impact of military operations (see Fairford Firepower, page 30). Effective employment of all munitions, especially PGMs, requires good intelligence and mission planning.
Laser-guided bombs, missiles and TV/Infra-red homing munitions have demonstrated their utility in numerous conflicts as compared to unguided munitions. However, TV systems cannot be used at night, while laser and MR sensors are restricted by clouds, fog, rain and snow. Following the 1991 Gulf War, the US military services combined several munitions development programmes in search of a weapon which could be delivered under all-weather conditions from beyond the lethal range of terminal SAMs and AAA, yet had sufficient accuracy and low cost to replace unguided bombs.
Technology advancements during the past 20 years led to two new developments — small and inexpensive inertial navigation systems and the USAF Navstar Global Positioning System (GPS). Both of these developments work together in the JDAM to revolutionise strike warfare. Today defence planners no longer ask: ‘How many sorties will it take to destroy a target?’ but ‘How many targets can we hit with this sortie?’ During the 1980s and early 1990s, technology development funded by the USAF and US Navy led to miniaturised and low cost inertial guidance systems (INS). Testing demonstrated that bombs which included an INS could be controlled by guidance fins on a bomb to achieve a Circular Error Probable (CEP) of less than 164ft (50m).
The INS notes wind changes to the flight path and other deviations following an initial alignment using data from an aircraft weapons system fed just before release. With data from navigation satellites provided during the flight of the bomb, this performance could be substantially improved.
The GPS system includes two dozen satellites transmitting signals that provide accurate position information to commercial, civil and military users equipped with the appropriate receiver. When a GPS receiver is combined with the INS, it provides position updates until impact. This guidance will place the bomb, especially the large and highly destructive 2,0001b (907kg) Mk-84/BLU-109, within the lethal radius of most potential targets. When released from medium altitude and subsonic speed, the JDAM can hit targets more than a dozen miles (18km) from the launch aircraft.
Boeing and Northrop-Grumman were industry leaders in the area of inertially aided/GPS munitions — the latter firm won a demonstration programme which fielded the GPS-aided Munition (GAM) which was tested on the B-2. In 1994, following an extensive competition, the USAF awarded Martin Marietta and McDonnell Douglas contracts to design and demonstrate a Joint Direct Attack Munition (JDAM). In October 1995, McDonnell-Douglas (today Boeing) was selected as the winner of the development and production programme.
The JDAM weapons system is a low-cost guidance kit which is fitted to existing free-fall
Mk-83 and BLU-110 1,0001b (450kg) bombs plus Mk-84 and BLU-109 2,0001b (900kg) bombs to improve their accuracy. Although less precise than laser-guided bombs, JDAMs offer a good degree of accuracy — 42ft (13m) as against 16ft (5m) for a Paveway III LGB -plus all-weather capability. In addition, attacking aircraft have greater operational flexibility since there is no need for target designation or visual acquisition, nor the need to remain in the target area to guide the bomb to impact via data link.
Testing and deployment
The JDAM test programme began in October 1996, and more than 250 weapons were dropped from B-l, B-2, B-52 bombers and F-16 and F/A-18 tactical aircraft. During these tests the weapon demonstrated a 95% success rate and achieved an average accuracy of 31ft 6in (9.6m) against its 42ft (13m) requirement. When the conflict in Kosovo began, the test programme was continuing and Boeing had delivered less than 1,000 development and early production models of the weapon. Operational testing had already certified the JDAM on USAF B-l and B-2 bombers and this effort is still in process for tactical aircraft. The US plans to certify the JDAM on USAF B-52s, F-15Es , F-16s and F-l 17s, plus USN/USMC F/A-18s, F-14s and the AV-8B (eventually the F-22 and JSF will be added). Licences for the export of the JDAM have already been approved.
The initial government estimate of the unit cost of a JDAM kit was $40,000 each. Boeing was able to deliver the weapon for considerably less than that amount, due to innovative development strategies, production concepts and close teamwork with suppliers, including Honeywell, Rockwell Collins and HR Textron. The JDAM kit, designated GBU-31 for the
2,0001b (907kg) and GBU-32 for the 1,0001b (454kg) weapons, includes a tail section which houses the guidance unit and GPS receiver which bolts onto a bomb, strakes to provide lift, guidance fins, and an electrical connection to the launch aircraft. These components are all packaged into a sealed container. The USAF plans to buy some 62,000 JDAM kits and the USN 25,000 and there are also a large number of international orders expected. Boeing is now developing a 5001b (227kg) Mk-82 version of the JDAM and additional variants which will extend the weapons range to 35miles (56km) and add improved guidance and warhead options.
During Operation Allied Force, B-2A bombers have been flying global power missions from Whiteman AFB in Missouri with the aid of air-to-air refuelling to strike multiple targets within Yugoslavia using JDAMs. The B-2 can deliver up to 16 Mk-84/BLU-109 JDAMs and has dropped more than 500 of these weapons with impressive accuracy since the start of NATO air action in March. This equates to over 1,000,0001b (453,600kg) of ordnance, all of which is reported to have been on target. Dollar for dollar, this is far better value for money than dropping unguided munitions in hope of hitting a target.
The B-1B Lancers of the 77th BS which are deployed to RAF Fairford are the latest Conventional Munitions Upgrade Program (CMUP) Block D aircraft which are also capable of carrying the JDAM. So far they have not used the new weapon, but they have the capacity to carry 24 JDAMs, eight more than the B-2A.
Combined with cruise missiles and other new systems under development, such as the Wind Corrected Munitions Dispenser (WCMD), Joint Stand Off Weapon (JSOW) and Joint Air-to-Surface Stand-off Missile (JASSM), JDAM is revolutionising air warfare. No enemy will be safe from strike, and at the same time, these highly accurate weapons will safeguard both crews and innocent civilians.