A Swedish firm has successfully tested using an American SDB smart bomb fired from a MLRS (multiple launch rocket system). Called this hybrid weapon GLSDB (Ground Launched Small Diameter Bomb) the rocket propelled bomb has a range of 150 kilometers. MLRS was designed to fire a 309 kg (680 pound) 227mm rocket. The latest version is (GMLRS) is GPS guided with a max range of 85 kilometers (and the ability to land within ten meters/31 feet of its intended target). The GLSDB guidance system was able to function despite the rapid acceleration of a rocket launch. The GLSDB provides more capability for MLRS systems at low cost.
The U.S. Air Force developed the 285 pound (129 kg) Small Diameter Bomb (SDB). The official story was that this GPS guided smart bomb was needed for urban warfare. The smaller blast (17kg/38 pounds of explosives, compared to 127 kg/280 pounds for the 500 pound bomb) from an SDB resulted in fewer civilian casualties. Friendly troops can be closer to the target when an SDB explodes. While the 500, 1,000 and 2,000 pound bombs have a spectacular effect when they go off, they are often overkill. The troops on the ground would rather have more but smaller GPS bombs available. This caused the 500 pound JDAM to get developed quickly and put into service. But the smaller SDB was always a mystery because so few were actually used.
SDB wasn’t just a smaller bomb, it also has a hard steel, ground penetrating, front end that can penetrate nearly two meters (six feet) of concrete. Not much use for that in urban warfare. But such a capability is very useful for taking out underground installations, particularly the entrances and air intakes. Still, there have not been many targets like that since September 11, 2001.
Despite all this in 2006 the air force finally got the SDB into service, in Iraq. The SDB was supposed to enter service in 2005, in the wake of the 2004 introduction of the 500 pound JDAM. But there were many technical problems with the more complex SDB. That's because this was not just another "dumb bomb" with a GPS guidance kit attached. The SDB had a more effective warhead design and guidance system. Its shape is more like that of a missile than a bomb (1.78 meters/70 inches long, 190 millimeters in diameter), with the guidance system built in. In the last few years, development work has continued. In 2009, for example, there was a change in the software of the SDB so that it could be used like a JDAM. That is, it could be dropped from an aircraft while directly above the target. The SDB was built as a glide bomb, which was dropped over a hundred kilometers from the target, then glided most of that distance before diving on the target. This resulted in complaints from troops below, who had to wait longer for a SDB to hit. The SDB was often preferred, especially in urban areas, because it had less bang than a 500 pound JDAM. But not when it took so long to arrive. Later improvements enabled SDB to reliably hit moving targets. Still not a lot of demand. GLSDB may change all that, although it won’t provide more work for the air force.