The new BRU-78 Dual Carriage System allows the MQ-9 Reaper to carry two bombs on a single hardpoint, doubling the number of free fall weapons it can employ in combat.
The U.S. Air Force has released photos of the first test of the GBU-39 Small Diameter Bomb being loaded on the MQ-9’s newest weapons employment dispenser system, called the Dual Carriage System. The GBU-39 SDB has been mentioned multiple times in the past as one of the planned new additions to the Reaper’s arsenal.
One of the first mentions of this came in 2017, when the Air Force announced on Nov. 27 a $17.5 million contract to General Atomics Aeronautical System (GA-ASI), the manufacturer of the Remotely Piloted Aircraft (RPA), to perform the integration. Strangely, a day later, the Department of Defense published a correction stating that the contract “has not yet been awarded.”
The contract notice specifically mentioned the GBU-39B/B Laser SDB as the weapon to be integrated. The original deadline for the contract set at the time, before the correction, was 2021. It is unclear when the contract was finally awarded and which were the reasons behind the correction to the award notice.
The testing
The first load test, according to the photos released, was conducted at Creech Air Force Base, Nevada, on the night of Mar. 12, 2025, although the photos were only released on Mar. 21. The captions mention that the test saw the 432nd Maintenance Group Weapons Standardization team, in collaboration with Air Combat Command and the 556th Test and Evaluation Squadron, working on the loading procedure.
The MQ-9 is shown carrying the Dual Carriage System on the inner hardpoint of the left wing. The system allows to load two weapons side-by-side, similarly to the M299 launcher already used by the Reaper to carry the AGM-114 Hellfire missile.
Interestingly, even if the original contract only mentions the Laser SDB, the photos show that two Laser SDB and two standard SDB were prepared for the test. Moreover, the weapons were live, as denoted by their yellow markings. Although only one bomb was clearly shown being installed on the aircraft, more weapons were loaded later, as demonstrated by a photo of the Airmen working also on the other side of the aircraft, loading a second weapon.
The choice of performing the test at night is also notable, but yet uncommon for such tests. However, this might replicate the conditions seen during many of the Integrated Combat Turn training events that the service has conducted lately, perhaps in order to have conditions closer to an operational scenario.
The Dual Carriage System
Before the introduction of the Dual Carriage System, the RPA could only load a single bomb per pylon. The GBU-39 already has a rack to load multiple units, the BRU-61, however it is used only by combat aircraft.
While the BRU-61 loaded with four GBU-39s weights 1,397 lb (634 kg) and thus falls within the reported 1,500 lb (680 kg) reported limit of the two inboard weapons, this would restrict the capabilities of the MQ-9. In fact, loading two BRU-61s for symmetry would get close to the 3,750 pounds (1,701 kilograms) external payload limit of the aircraft, influencing the choice of the other payloads.
The use of the Dual Carriage System would allow greater flexibility in the selection of the payload, also allowing the Reaper to carry a wider array of munitions for different needs. While specifications of the systems are not known, a key difference from the BRU-61 noted from the photos is that the weapons are loaded only after the rack has been installed on the aircraft. The BRU-61, on the other hand, is loaded with the four GBU-39s already attached to it.
The BRU-78
The Air Force has not released further details about the Dual Carriage System. However, an online search revealed that the system is produced by L3Harris and designated BRU-78 Dual Carriage System.
A brochure released in 2019 on the company’s website reveals that the system is designed for use on large unmanned aerial vehicles (UAVs) and light attack armed reconnaissance/ counterinsurgency (LAAR/COIN) platforms. The brochure also mentioned that, at that time, the BRU-78 was being qualified for flight on the MQ-9 Reaper.
The company says the BRU-78 is designed for weapons of the 500-pounds class and smaller, and used both the conventional MIL-STD-1760 and Universal Armament Interface (UAI) communications. The BRU-78 integrates two L3Harris-designed BRU-71 ejector units as the mechanical interface to install the weapons.
Among the weapons intended to be used with the BRU-78 are the GBU-12/49/59 laser-guided bombs, GBU-38/52/54 Joint Direct Attack Munitions (JDAMs) and GBU-39/53 Small Diameter Bombs. It is unclear if the Air Force, following the completion of the GBU-39 testing, will test also the other weapons on the new rack, since they already are in the MQ-9’s inventory.
The GBU-39 Small Diameter Bomb
As we often reported, the SDB is a small 250-lb multipurpose, insensitive, penetrating bomb with a blast-fragmentation warhead for stationary targets. One of its distinctive features is the presence of deployable wings for extended standoff range that open upon release.
The wings allow the GPS-guided bomb to glide for several miles before hitting the target with accuracy. In fact, launched at high-speed from high altitude, the GBU-39 can travel for as much as 50 miles, allowing the attack plane to remain outside the range of most SAM (Surface-to-Air Missile) batteries.
The weapon is being extensively used in Ukraine since early 2024. It is being reported that the GBU-39 has demonstrated itself to be largely resilient to the Russian electronic warfare systems, with Ukraine claiming about 90% of the SDBs employed have struck their assigned targets.
