The U.S. Air Force finally got its 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. These two efforts were designated GBU-40 and GBU-53 and after three years of delays (for tweaking and testing, a cycle repeated several times until this year the GBU-53 designers won because they finally got a promising concept to actually work, three years after it was announced as almost ready (“almost” was often not mentioned). In recognition of the GBU-53 design was finally doing everything SDB II promised but never quite delivered the SDB II/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, it is one but with a better press agent.
The SDB could use some more effective marketing and a new version that actually delivers on impressive promises seemed to deserve a sexy and descriptive name. 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 datalink 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 the fighter (especially F-35) pilot 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 has been 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 earlier model (SDB I) that can 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 (also known as SFB II that actually works) 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 (about $70,000 for SDB I and about $300,000 for GBU-53 SDB II). The small wings allow the SDB to glide up to a hundred kilometers (from high altitude). SDB also 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 500 pound bomb.
The SDB is considered the next generation of smart bombs and the more compact design allows more to be carried. Thus, F-15/16/18 type aircraft can carry 24 or more SDBs. 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.