Small Diameter Bombs GBU-39/B | GBU-39A/B | GBU-53/B


GBU-39 small diameter bomb

GBU-39/B SDB I  |  Specs  |  Video

GBU-39A/B FLM (Focused Lethality Munition)  |  Specs

GBU-53/B StormBreaker (SDB II)  |  Specs  |  Video

Collaborative Small Diameter Bomb (CSDB) 'Golden Hoard'

Ground Launched Small Diameter Bomb (GLSDB)


Small diameter bombs represent a newer approach to target destruction. Instead of relying on the brute-force of a large warhead which can cause a lot of collateral damage they feature a lower yield warhead in a smaller package, a 250 lb (113 kg) class weapon. A significant advantage with the smaller size is that more of them can be carried on each aircraft. Crucial to this equation is the BRU-61/A bomb rack which can put four small diameter bombs on each compatible weapon station. For the war planner, this means the number of targets attacked with each sortie can be much greater. For stealth aircraft with internal weapon bays like the F-22 and the F-35 this substantially increases their load-out of air-to-ground weapons while maintaining their stealthy profile.

After launch, wings flip out into a diamond shaped configuration, giving the SDB a standoff range of 40 - 60 nm or 46 - 69 mi (74 - 111 km) - the high end of the range is for a high-altitude launch. The small diameter bomb is also incredibly accurate, hitting within a radius of 1 meter (~3 ft). With a penetration of more than 3 ft (1 m) through steel-reinforced concrete the GBU-39/B is also handy for bunker busting - for more about bunker busting weapons click here. To ensure that the weapon reaches the target successfully, despite enemy countermeasures, it has the latest SAASM/AJ (Selective Availability Anti-Spoofing Module / Anti-Jam) technology. All these traits make the GBU-39/B SDB I useful against a wide variety of fixed and stationary targets, for moving targets the GBU-53/B StormBreaker (SDB II) is ideal.

A article dated September 22, 2022 on the Saab website states that more than 20,000 small diameter bombs have been produced since 2006 and 10,000 used in combat. It also said that the SDB I is used by the U.S. Air Force, the Norwegian Air Force, and thirteen other countries.

GBU-39A/B FLM (Focused Lethality Munition)

The GBU-39A/B FLM (Focused Lethality Munition) is a version of the small diameter bomb that has a carbon-fiber bomb body provided by Aerojet Rocketdyne which disintegrates upon detonation rather than fragments as a steel bomb case does, and a multi-phase blast explosive warhead developed by the Air Force Research Laboratory (AFRL) and the Lawrence Livermore National Laboratory (LLNL). This reduces collateral damage considerably by keeping metal fragments from flying everywhere (depending on bomb size these fragments can travel hundreds of feet at high speed and be quite deadly.) The warhead focuses the blast and produces more devastating effects in a smaller space, making the FLM ideally suited to taking targets out in crowded urban areas and in close contact air support scenarios. The Focused Lethality Munition complements the GBU-39/B and fits in the same fashion to the BRU-61/A bomb rack.

The first 50 FLM weapons were delivered to the Air Force in March 2008, according to the Air Force Armament Museum. Boeing reported that it delivered the 500th and final FLM to the US Air Force in December 2013, in a Dec. 19, 2013 news release. The same press release stated that the Air Force has dropped 23 FLMs in combat operations and has a 23 for 23 mission-success rate.

GBU-39 takes out a protected target aircraft

GBU-39/B takes out a protected target aircraft

BRU-61/A Bomb Rack Unit (Carriage System)

The BRU-61/A bomb rack weighs 320 lb (145 kg) empty, this increases to 1,460 lb (664 kg) when loaded with four GBU-39/B small diameter bombs. With a length of 143 inches (3.6 m) and height and width of 16 in (40.6 cm), the BRU-61/A fits almost every delivery platform, including the F-15E, F-16, F-22A, F-35, B-1, B-2, B-52, and unmanned combat aircraft like the MQ-9 Reaper. In real world terms, this means that four SDBs can be carried in place of a single 2,000 lb (907 kg) bomb when using the BRU-61/A bomb rack.

Source of specs for BRU-61/A: Boeing

BRU-61/A bomb rack with four SDBs

BRU-61/A bomb rack loaded with four GBU-39 SDBs

Collaborative Small Diameter Bomb (CSDB) 'Golden Hoard'

The Golden Hoard Vanguard program is concerned with creating networked, collaborative and autonomous (NCA) weapon capabilities through real-live weapon testing and using digital environments (simulations). It features standard small diameter bombs (SDB I) modified into swarming munitions in a collaborative network. Rules set beforehand in the CSDB can be executed without human intervention to maximize the results of the mission and, along with other collaborative small diameter bombs, overwhelm the defenses. The Golden Hoard saw a successful test at the White Sands Missile Range in New Mexico on May 25, 2021. Two F-16s from the 96th Test Wing Eglin Air Force Base simultaneously released six CSDB weapons (four from one aircraft and two from the other.)

During the test, two weapons performed a synchronized time on target (STOT) attack against a single target. Also, a ground station sent an In-Flight Target Update (IFTU) to the flight weapons to engage a new high priority target - this interfacing of Golden Horde munitions with the larger Joint All-Domain Command and Control (JADC2) network was a key goal of the test. Two other collaborative small diameter bombs were synchronized on two targets.

Collaborative Small Diameter Bombs on a F-16

Four Collaborative Small Diameter Bombs on a F-16

Ground Launched Small Diameter Bomb (GLSDB)

A weapon system developed by Boeing and the Saab Group, the 600 lb (270 kg) Ground Launched Small Diameter Bomb (GLSDB) is a tremendous addition for ground forces who need a long range precision strike capability. Combining two proven elements, the M26 rocket with a GBU-39/B SDB I, the GLSDB can be launched from different ground vehicles and configurations including the M270 MLRS (Multiple Launch Rocket System) and the M142 HIMARS (High Mobility Artillery Rocket System). After launch, when the GLSDB reaches the right flight configuration (high enough speed and height), the small diameter bomb separates from the rocket and continues on with wings deployed, for a maximum range of 150 km (93 mi).

Click on the Video below to see the GBU-39 SDB I in action.

Click here to see specification tables.

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GBU-53/B StormBreaker (SDB II)

While it relies on a GPS enhanced Inertial Navigation System (INS) to get in the vicinity of the target, the StormBreaker has a tri-mode seeker with millimeter-wave (MMW) radar, uncooled imaging infrared (IIR), and a semi-active laser sensor, for the actual target engagement. This unique combination of sensors allows the GBU-53/B to take out stationary and moving targets in adverse weather on land and at sea and in low visibility conditions - like through smoke or dust. The 105 lb (48 kg) multi-effects warhead has shaped charge jets, fragmentation and blast charge effects, and is designed to cause low collateral damage yet be capable of taking out armored vehicles, including main battle tanks.

The GBU-53/B is net enabled with a two-way data link that allows for re-targeting/updating and abort options from friendly aircraft and ground controllers. It can also conduct reconnaissance as it glides toward the target and spot/classify other targets for possible follow-up strikes. All this comes at a cost and the StormBreaker Bomb is some five times the price per copy over the GBU-39/B SDB I. See the specifications below to see more about the cost of these weapons.

Integrated with the F-15E, work is ongoing to equip the US Navy's F/A-18E/F and the F-35B and F-35C variants of the F-35 with the StormBreaker. Objective aircraft for weapon integration include the F-35A, F-16, F/A-18E/F, A-10, F-22, B-2, B-1B, B-52 and the MQ-9 drone. The F-35 can carry a total of 24 GBU-53/B (eight internally and, when stealth is not desired, 16 externally), while the F-15E Strike Eagle can carry at least 20 StormBreakers held by five BRU-61/A bomb racks.

GBU-53/B StormBreakers

StormBreakers mounted on F-15E Strike Eagle (Air Force photo)

Watch the short video below to see a F-15E release a single GBU-53/B StormBreaker Bomb:

Click here to see specification tables.

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GBU-39 small diameter bomb



DesignationGBU-39 SDB IGBU-53/B StormBreaker (SDB II)
Typeprecision-guided glide bombprecision-guided glide bomb
Cost~$40,000 1~$213,000 2
First FlightMay 23, 20032012
IOCOct. 2, 2006Sept. 23, 2020
In CombatOct. 2006 3?
GuidanceGPS/INSGPS/INS & tri-mode seeker 4
FuseESAF 5smart fuse
Warheadmultipurpose penetration,
blast-fragmentation 6
multi-effects 7
Warhead Weight206 lb (93 kg)105 lb (48 kg)
Total Weight285 lb (130 kg)204 lb (92.5 kg)
Wing Span63.3 in (1.61 m)68 in (1.73 m)
Length70.8 in (1.8 m)69 in (1.75 m)
Diameter7.5 in (0.19 m)6-7 in (0.15 - 0.18 m)
Rangestandoff: more than 46 mi (74 km) 8standoff: >45 mi (72 km) to >62 mi (100 km) 9
Accuracywithin a radius of 1 m (~3 ft)highly accurate

1 The Air Force fact sheet states that the GBU-39/B costs $40,000 per unit.
2 U.S. Air Force awarded Raytheon a $320 million contract to produce and deliver 1500 StormBreaker Bombs.
3 GBU-39/B (SDB I) first employed by an F-15E over Iraq in October of 2006.
4 GBU-53/B tri-mode seeker includes millimeter-wave (MMW) radar, uncooled imaging infrared (IIR), and semi-active laser sensor.
5 GBU-39 has a ESAF (Electronic Safe/Arm Fuse) cockpit selectable functions, including air burst and delayed burst options.
6 The GBU-39A/B FLM (Focused Lethality Munition) has a composite (carbon-fiber) bomb body for ultra low fragmentation.
7 The GBU-53/B multi-effects warhead includes shaped charge jets, fragmentation and blast charge effects.
8 The Boeing website claims a maximum range of greater than 60 nautical miles or 69 miles (111 km) for the GBU-39.
9 The StormBreaker's range of >45 mi (72 km) is for mobile targets with >62 mi (100 km) for fixed targets.

Estimates vary by source.

Specifications info from US Air Force, the Air Force Armament Museum, Boeing, Raytheon, and Saab.
Metric values calculated with the help of Convertworld.

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More Links

Raytheon's StormBreaker Page

Boeing's Precision Engagement

Aerojet Rocketdyne Composite Bomb Body Page

Air Force Research Laboratory

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