GBU-39 Small Diameter Bomb
The GBU-39/B Small Diameter Bomb (SDB) is a  precision-guided glide bomb that is intended to provide aircraft with the ability to carry a higher number of more accurate bombs. Most US Air Force aircraft will be able to carry (using the BRU-61/A rack) a pack of four SDBs in place of a single  bomb. It first entered service in 2006. The Ground Launched Small Diameter Bomb (GLSDB) was later developed to enable the SDB to be launched from a variety of ground launchers and configurations. Description

The original SDB is equipped with a GPS-aided inertial navigation system to attack fixed/stationary targets such as fuel depots, bunkers, etc. The second variant, Raytheon's GBU-53/B SDB II, will include a thermal seeker and radar with automatic target recognition features for striking mobile targets such as tanks, vehicles, and mobile command posts. The small size of the bomb allows a single strike aircraft to carry more of the munitions than is possible using currently available bomb units. The SDB carries approximately  of AFX-757 high explosive. It has integrated "DiamondBack" type wings which deploy after release, increasing the glide time and therefore the maximum range. Its size and accuracy allow for an effective munition with less collateral damage. Warhead penetration is  of steel reinforced concrete under 3 ft of earth and the fuze has electronic safe and fire (ESAF) cockpit selectable functions, including air burst and delayed options. The SDB I has a circular error probable (CEP) precision of . CEP is reduced by updating differential GPS offsets prior to weapon release. These offsets are calculated using an SDB Accuracy Support Infrastructure, consisting of three or more GPS receivers at fixed locations transmitting calculated location to a correlation station at the theatre Air Operations Center. The corrections are then transmitted by Link 16 to SDB-equipped aircraft. Alternative guidance and warheads
In November 2014, the U.S. Air Force began development of a version of the SDB I intended to track and attack sources of electronic warfare jamming directed to disrupt the munitions' guidance. The home-on-GPS jam (HOG-J) seeker works similar to the AGM-88 HARM to follow the source of a radio-frequency jammer to destroy it. In January 2016, the Air Force awarded a contract to Scientific Systems Co. Inc. to demonstrate the company's ImageNav technology, a vision-based navigation and precision targeting system that compares a terrain database with the host platform's sensor to make course corrections. ImageNav technology has demonstrated target geo-location and navigation precision within three meters. In January 2016, Orbital ATK revealed that the Alternative Warhead (AW), designed for the M270's GMLRS to achieve area effects without leaving behind unexploded ordnance, had been successfully tested on the SDB. Development
In 2002, while Boeing and Lockheed Martin were competing to develop the Small Diameter Bomb, Darleen A. Druyun – at that time Principal Deputy Assistant Secretary of the Air Force for Acquisition and Management – deleted the requirement for moving target engagement, which favored Boeing. She was later convicted of violating a conflict of interest statute. In May 2009, Raytheon announced that it had completed its first test flight of the GBU-53/B Small Diameter Bomb II, which has a data link and a tri-mode seeker built with technology developed for the Precision Attack Missile. In August 2010 the U.S. Air Force awarded a $450 million contract for engineering and development. Although unit costs were somewhat uncertain as of 2006, the estimated cost for the INS/GPS version was around US$70,000. Boeing and the Italian firm Oto Melara signed a contract covering the license production of 500 GBU-39/B (INS/GPS) and 50 BRU-61/A racks for the Aeronautica Militare, at a cost of nearly US$34 million. Timeline
 October 2001 – Boeing is awarded SDB development contract in addition to Lockheed Martin to compete to become the prime contractor. April 2005 – Boeing awarded contract as Prime Contractor, beating Lockheed Martin. September 2005 – Small Diameter Bomb certified for operational test, evaluation. September 2006 – SDB team deliver the first SDBs to the USAF. October 2006 – Initial Operational Capability declared for SDB on the F-15E Strike Eagle. October 2006 – First use in combat. February 2008 – 1,000th SDB I and first 50 FLM delivered. September 2008 – Israel received approval from the US Congress to purchase 1,000 bombs. December 2008 – Reportedly used against Hamas facilities in the Gaza Strip, including underground rocket launchers. January 2009 – Unnamed Boeing official stated that they have yet to deliver any SDBs to Israel. June 2010 – FMS request by the Netherlands for 603 units and support equipment valued at US$44 million. August 2010 – U.S. Air Force selects Raytheon's GBU-53/B for Small Diameter Bomb II Program. 2014 – Work begins on home-on-GPS jam. May 2015 – GBU-53/B SDB II approved by Pentagon for production and deployment on the F-15E. April 2016 – FMS request by Australia for 2,950 units and support equipment valued at US$386 million. Aircraft 
The GBU-39/B began separation tests on the F-22 Raptor in early September 2007 after more than a year of sometimes difficult work to integrate the weapon in the weapons bay and carry out airborne captive carry tests. The SDB is currently integrated on the F-15E Strike Eagle, Panavia Tornado, JAS-39 Gripen, F-16 Fighting Falcon, F-22 Raptor and AC-130W. Future integration is planned for the F-35 Lightning II, A-10 Thunderbolt II, B-1 Lancer, B-2 Spirit, B-52 Stratofortress and AC-130J. Other aircraft, including UCAVs, may also receive the necessary upgrades. The General Atomics Predator C is also planned to carry this weapon. Variants

GBU-39A/B – SDB Focused Lethality Munition (FLM)
Under a contract awarded in September 2006, Boeing developed a version of the SDB I which replaces the steel casing with a lightweight composite casing and the warhead with a focused-blast explosive such as dense inert metal explosive (DIME). This should further reduce collateral damage when using the weapon for pin-point strikes in urban areas. On 28 February 2008, Boeing celebrated the delivery of the first 50 FLM weapons. The USAF intends to use the same FLM casing on a weapon of . In December 2013, Boeing delivered the last of the 500 FLMs under contract. GBU-39B/B – Laser SDB
In mid-2012, the U.S. Senate recommended zeroing out funding for the GBU-53/B SDB II due to fielding delays with the F-35 Lightning II. With the delay in SDB II fielding, Boeing recommended an upgrade to their SDB as a temporary gap-filler to get desired performance at a fraction of the cost. Called the Laser Small Diameter Bomb (LSDB), it integrates the laser used on the JDAM to enable the bomb to strike moving targets. Boeing began testing the LSDB in 2011 and successfully hit targets traveling . In June 2013, Boeing was awarded a contract to develop and test the LSDB. The contract is for phase one part two engineering, integration and test, and production support and an LSDB Weapon Simulator. Boeing says the LSDB can be built at a lower cost than the planned Raytheon GBU-53/B SDB II, as it will use the same semi-active laser sensor as the JDAM to hit moving and maritime targets. However, Boeing admits that it does not have the capability to engage targets in zero-visibility weather, as it lacks the SDB II's millimeter wave radar. The Laser SDB began fielding with the U.S. Special Operations Command in 2014. Ground Launched Small Diameter Bomb (GLSDB)

Operators

Current operators 

 : Foreign Military Sale of up to 2,950 GBU-39 (SDB 1), and 50 Guided Test Vehicles with GBU-39 (T-1)/B (Inert Fuze) for an est. cost of $386 million was approved in April 2016, with bombs delivered to RAAF in 2019.
 : In 2012 Israel purchased munitions from the United States at a total value of $1.879 billion, which included 3,450 GBU-39/B (SDB 1), plus 4,100 GBU-39/B purchased in 2015 as part of another munitions purchase. : In 2010 Italian company OTO Melara signed a $34 million contract with Boeing to manufacture the SBD-1 for the Italian Air Force. : In 2010 the Netherlands purchased 603 GBU-39 (SDB 1) for an estimated cost of $44 million. : In October 2013, Saudi Arabia purchased various munitions from the US, including 1,000 GBU-39 (SDB 1). In Dec 2020 a request to purchase 3,000 GBU-39 (SDB 1) was approved by the US Government. : In 2013 South Korea made two purchases of the GBU-39, as part of a purchase of weapons for F-15 SE including 542 GBU-39/B and weapons for the F-35 aircraft, of another 542 GBU-39/B. : In 2019, Sweden ordered the GBU-39, to be deployed from the JAS 39 Gripen. : the United States is the major operator of the GBU-39 (SDB 1). Future operators 

 : In 2019 The Bahraini Government purchased as part of sale of a number of weapons for the Royal Bahraini Air Force's F16 aircraft fleet 100 GBU-39/B (SDB 1). : In 2019 Bulgaria agreed to purchase 8 F-16C/D Block 70/72 aircraft with 28 GBU-39 (SDB 1) and other munitions. By 2020 Bulgaria had paid 100% of the $1.673 billion cost, however delivery is not expected until 2026. In 2022 Bulgaria was approved to purchase another 8 F-16 C/D Block 70 aircraft, with another 28 GBU-39 (SDB 1), for the same cost. :  in 2019 Morocco requested to purchase 25 F-16C/D Block 72 aircraft, including 60 GBU-39/B (SDB 1). : In 2022, a request by NATO to purchase precision Guided Munitions, including 279 GBU-39/B (SDB 1) was approved by the US Government. : In February 2023 the US Government has agreed to send Ground Launched Small Diameter Bombs (GLSDBs) to Ukraine, set to arrive no earlier than Autumn 2023.
 : In 2013 a requested to purchase 5,000 GBU-39/B (SDB 1) as part of a sale of various Munitions was approved. In 2020 request to purchase another 2,500 GBU-39/B (SDB 1) was accepted. See also
 H-4 SOW – Pakistani precision guided glide bomb
 Spice (bomb) – Israeli precision bomb convertible unguided to guided
 KGGB – South Korean precision guided glide bomb

References

External links

GBU-39 Small Diameter Bomb / Small Smart Bomb - Global Security
Small Diameter Bomb SDB Focused Lethality Munition (FLM) - Global Security
GBU-39/40/42/B Small Diameter Bomb I/II

Guided bombs of the United States
Boeing
Military equipment introduced in the 2000s