December 5, 2022: Boeing is the developer and producer of the GMLRS guided missile used so frequently in Ukraine. It and Swedish firm Saab have developed a new weapon called GLSDB (Ground-Launched Small Diameter Bomb) The design concept is simple. Take the 227mm rocket motor that propels the GMLRS and use it to launch the latest version of the U.S. Air Force SDB (Small Diameter Bomb), the GBU-53 Stormbreaker.

Initially, the SDB was seen as the next generation of smart bombs and is a more compact design of the classic 227 kg (500-pound) unguided bomb. The streamlined shape of the SDB, which carried the GPS guidance system and other guidance components internally) allowed more to be carried by F-15/16/18 type aircraft, which can carry 24 or more SDBs each. The SDBs are carried on a special carriage which holds 4 of them instead of one bomb of more traditional shape. The carriage is mounted on a bomber just like a single larger (500, 1,000, or 2,000) pound bomb would be. However, this feature was rarely needed in combat situations because one smart bomb does the work of hundreds of unguided ones. There are also a lot of other guided weapons out there.

SDB has a hard front end that can punch through nearly three meters (eight feet) of rock or concrete and a warhead that does less damage than the usual dumb bomb (explosives in a metal casing). That’s because the SDB warhead carries only 17 kg (38 pounds) of explosives, compared to 127 kg (280 pounds) in the conventional 227 kg (500-pound) bomb.

Boeing/Saab are seeking a contract to deliver production models of GLSB to Ukraine by February 2023. Ukraine is interested because GLSBD can be fired from HIMARS or any other GMLRS launch vehicle and has a range of 150 kilometers. Moreover, it is more precise than GMLRS because Stormbreaker has multiple guidance systems that enable it to hit moving targets, including ships at sea and do so at night and in any weather.

Stormbreaker entered service in 2018 as the latest version of the SDB II (Small Diameter Bomb also known as GBU-53) into service. This version can identify, track and hit a moving target on the ground in any weather and at night. Originally this version was just called SDB II and declared to be in service. But in fact, there were problems getting the three targeting sensors to work reliably and two manufacturers were set to work developing different tech to make it work. That took three years of tweaking and testing, a cycle repeated several times until 2018 when the GBU-53 designers got their novel targeting system to work reliably. In recognition of this the GBU-53 was given an official nickname; Stormbreaker. Much catchier than SDB, or even (or especially) SDB II. Publicizing the new, improved Stormbreaker does cause a bit of confusion for those who do not follow the SDB saga regularly. Most of those who look into Stormbreaker eventually realize it is not just similar to the SDB, but has a better press agent.

SDB II has been in development since 2005 and announced as ready several times, at least until the last round of Operational Tests were conducted and, as often happens during these realistic (“operational”) tests something goes wrong. In other words, SBB II was, for a long time, ready to go, but not quite ready for prime time (actual combat). At least not for missions requiring certain features that were having Operational Test problems.

When first announced in 2005 SDB II was described as possessing multiple sensors and a data link that enabled it to hit vehicles going at high speed and in bad weather. Sounded great but the repeated failures to get past the Operational Testing meant SDB II did not boost sales as much as anticipated. From the beginning, SDB II had an encrypted data link that enabled fighter (especially F-35) pilots to guide the SDB, with great precision, to hit moving targets. This communications capability enabled the SDB movement to be controlled via the air force's airborne Internet (Link 16), which means the “bomb driver” can be anywhere, even another aircraft or on the ground. The SDB II has three different guidance systems: radar, heat seeker, and homing on laser light bounced off the target. That means no matter what the weather or time of day there is a guidance system that will find the target. Even without human intervention, the three sensors enable SDB II to find targets in a cluttered and obscured (by weather or darkness) environment. Now it actually works but it was felt that a new name might overcome the shaky reputation the SDB II had earned.

Meanwhile, sales of the SDB were picking up, especially export orders. In late 2017, Australia ordered another 3,900 American SDB (GBU-39) for $209,000 each (including training and maintenance accessories and support). This order is for the SDB II (GBU-39B) for its F-35 fighters. This may well be modified to use the more capable GBU-53. In early 2016 Australia ordered 2,950 of the older model SDB I that could only hit stationary targets. These cost $131,000 each. The 130 kg (285 pound) SDB entered service in 2006 and so far over 20,000 SDB I and SDB II have been ordered or delivered, most for the U.S. Air Force.

A major reason for some countries (like Australia) are buying so many SBDs is the success of JMMBRU, a special internal bomb rack that enables the F-35 to carry eight SDBs internally. Australia is buying a hundred F-35s in part because when flying with all weapons carried internally the aircraft is nearly invisible to radar. In a less stealthy configuration, another 16 SDBs cab be carried externally giving the F-35 a maximum capacity for 24 of these smart bombs.

The U.S. Air Force completed development and testing the JMMBRU bomb rack in 2014. This made the F-35 a much more effective bomber, especially since the SDB has been upgraded that same year with hardware and software to enable it to hit moving targets as well as being more accurate. While the original SBD would land 5-8 meters (16-25 feet) of the aiming point the SDB II had guidance system options that enabled it to land within a meter (three feet). The SBD II began mass production in 2016 and Australia was already interested.

The SDB was supposed to be a revolutionary weapon and in many ways it was. But there was not as much demand as expected because there are so many other small, precision weapons available. With the appearance of Stormbreaker the F-35 will be an even more impressive ground attack aircraft.

The SDB is basically an unpowered missile which can glide long distances. This makes the SDB even more compact, capable, and expensive. While the original SDB I cost about $70,000 each, that went up to $300,000 for Stormbreaker. The small wings allow the SDB to glide up to a hundred kilometers (from high altitude).

Launching Stormbreaker from the ground (or even a ship at sea) using any GMLRS launcher provides long range precision firepower at relatively low cost. In 2017 the American marines demonstrated that GMLRS rockets could be launched from the flight deck of amphibious assault ships against land targets. This concept can use GLSDB to do the same, but also against enemy ships as well as land targets.

What initially seemed like a frankenmissile turned out to be an effective, low-cost way to deliver precision firepower over long distances.