OSMP Collection
The GBU-39 air-delivered bomb: a visual guide
This is the first in a series of articles using interactive 3D models to explain widely used munitions to a general audience. The model below highlights key parts of the GBU-39 air-delivered bomb and presents them alongside relevant entries from the OSMP archive of munition images from conflict zones.
The GBU-39 Small Diameter Bomb (SDB) is a guided air-delivered bomb in the 250-pound weight class, developed and predominantly produced by Boeing in the United States. The munition entered service in 2006, and has been produced in at least three variants, with at least two different warhead configurations. The standard warhead contains 37 pounds (16.8 kg) of high explosive composition— a relatively small payload for an air-delivered bomb, intended to minimise collateral effects and enable fighter aircraft to carry larger numbers of munitions.
The GBU-39 has been used extensively by U.S. forces and allies in in recent conflicts in Afghanistan, Lebanon and Ukraine and has been described as the Israeli military’s “weapon of choice” in its bombing campaign in Gaza. The unit cost for the standard GBU-39 variant, the GBU-39/B, is given by the U.S. Air Force as $40,000 USD.
How to identify the GBU-39
Certain parts of specific munition models may consistently survive impact and functioning as a result of their design or position within the device. These are referred to as ‘diagnostic remnants’, and can sometimes be used to identify the munition involved in a strike.
Click on a button below to view some of the key component parts of a GBU-39/B. Each part is described and presented alongside images from the OSMP archive.
What are the key components?
The nosecone, located at the front of the munition, is made from hardened steel—enabling the munition to penetrate more than three feet (0.9 m) of steel-reinforced concrete. The heavy, metal construction of this component means it typically survives the bomb functioning, despite its proximity to the explosive payload.
The warhead is the portion of the munition which carries its payload, and in this case includes the nosecone at the front of the munition. The GBU-39/B warhead uses a high explosive composition (HE) to generate blast and fragmentation effects, with the nosecone offering hard-target penetration. Weighing 206 pounds with 37 pounds of explosive content, the complete warhead rarely survives intact unless the munition fails to function as intended (i.e. does not detonate).
A folding wing assembly attached above the warhead section of the munition creates a distinctive V-shape when deployed. This wing configuration permits longer, flatter ‘gliding’ attack angles during strikes. These wings are often recovered after the explosion, because they can be sheared off as the bomb penetrates a structure before detonating—often resulting in them being found outside the building or floor where the munition impacted.
The fuzewell, located at the base of the warhead, hosts the munition’s fuze and is sometimes found intact after the munition explodes. When the fuze functions and the warhead detonates, the fuzewell is often ejected from the bomb’s body.
The tail actuation system is located at the rear of the munition—the farthest point from the explosive. In flight, the munition’s trajectory is adjusted by GPS and inertial guidance commands, which control the four hinged tail-fins. The tail actuation system, including the thermal battery, is often found partly or largely intact following the munition’s functioning.
A relatively small, precise bomb
GBU stands for ‘Guided Bomb Unit’, following a U.S. Air Force naming convention applied to guided, unpowered munitions. Whilst the ‘GBU’ prefix forms part of the designations of a number of other guided bombs — such as the GBU-31, GBU-32, and GBU-38 — the GBU-39 has no direct relation to other designs in the U.S. inventory.
The GBU-39 was first developed partly in an attempt to reduce the probability of collateral damage from airstrikes. In 1997, the U.S. Air Force Air Combat Command defined “a mission need for a miniaturized munition capability.” The GBU-39 was one of several weapons designed in response.
Falling in the 250-pound weight class (the GBU-39/B has a total weight of 268 lbs, or 122 kg), it is far smaller and lighter than the MK 82 (500 pound), MK 83 (1,000 pound), and MK 84 (2,000 pound) bombs that have formed the backbone of the U.S. military’s arsenal of air-delivered munitions for decades.
The introduction of a small, precise air-delivered munition also offered an additional military advantage: smaller munitions allow aircraft to carry out more strikes without returning to an airfield for re-arming. Most U.S. Air Force aircraft are able to carry a ‘pack’ of four SDBs in place of a single 2,000-pound class bomb. Two packs, for a total of eight GBU-39 bombs, can be carried under normal operational circumstances. Multiple munitions can also be employed against a single or multiple targets simultaneously.
The GBU-39 is guided using inertial navigation and GPS. While many air-delivered bombs typically use so-called ‘bolt-on’ guidance kits attached after the bomb is manufactured, the GBU-39’s bomb body and guidance system are combined as a single unit during the production stage. Target coordinates are communicated to the munition whilst it is fitted to an aircraft, and the bomb uses its onboard guidance to steer itself to the desired target after release. The guidance system also incorporates anti-jamming features, allowing the munition to be employed in areas under threat of enemy electronic warfare (EW) countermeasures.
Owing to its glide-wing design and other characteristics, the GBU-39 has a range of more than 110 km from its release point. This provides a ‘stand-off’ capability, reducing threats to aircraft delivering the munition.
The U.S. Air Force argues that the GBU-39 bomb “inherently reduces the probability of collateral damage”. One variant of the GBU-39, called the GBU/39A/B Focused Lethality Munition (FLM), was developed to reduce the likelihood of unintended casualties by using a ‘focused-blast’ explosive warhead which can restrict the spread of fragmentation during strikes. As a result of these features, the FLM variant of the SDB is often referred to as an “ultra-low collateral damage outside the blast zone” munition.
The GBU-39 is increasingly the weapon of choice for the Israeli military and was used in two recent mass-casualty events
— The New York TimesThe impact in Gaza
Whilst the GBU-39 is smaller than other air-delivered bombs and can be precisely targeted, its impact remains dependent on the nature of the target and the proximity of civilians and civilian objects. Particularly in heavily populated urban areas, employing any explosive munition can still pose risks to civilians and damage vital infrastructure.
Alma Al Osta, Arms Advocacy Manager with Humanity & Inclusion, has highlighted the risk of assuming using precise munitions is enough to protect civilians: “There is much more to protecting civilians than just choosing a precise weapon… if this weapon is used on open battlefields without the presence of civilians, then the risk would be smaller. But wars nowadays are fought in towns and cities where people live, children go to school, and civilians gather in markets.”
Over the course of the conflict in Gaza, the U.S. has shipped thousands of air-delivered bombs to Israel, only halting one shipment of 2,000-pound bombs when concerns arose over the ‘end use’ of the munitions nearly eight months into the conflict. The U.S. has continued to provide GBU-39 bombs without restriction, with 1,000 approved for delivery in May 2024.
Despite their smaller warhead and precision guidance, GBU-39 bombs have been linked to multiple incidents in which civilians were harmed.
On 10 August 2024, for example, an Israeli airstrike hit the Al-Daraj neighbourhood of Gaza City. Israel said it was targeting a Hamas command post. The strike damaged a school and a mosque, with health officials in Gaza reporting that 93 people sheltering in the area were killed. Videos posted by CNN showed extensive destruction and a number of bodies on the ground, as well as munition debris from a GBU-39 (a munition remnant from this strike features in the OSMP).
Remnants from GBU-39 bombs were also identified following a strike on 26 May 2024 at a camp for Palestinians in Rafah (a munition remnant from this strike features in the OSMP). Israel said it was targeting two Hamas commanders. Amnesty International found that at least 36 people were killed, including six children and four militants. The organisation said “the use of these munitions – which project deadly fragments over a wide area – in a camp housing civilians in overcrowded shelters is likely to have constituted a disproportionate and indiscriminate attack.”
External Resources
- Armament Research Services – Diagnostic Remnants of the GBU-39 Small Diameter Bomb (SDB)
- Boeing – Small Diameter Bomb (SDB)
- U.S. Air Force – GBU-39B Small Diameter Bomb Weapon System
- Royal United Services Institute – Precision Strike: A Brief Development History of PGMs
- GICHD – Explosive Weapon Effects: Final Report
