November28, 2006: Having just got it's 250 pound Small Diameter Bomb (SDB) into service, the U.S. Air Force is now spending $27 million to develop a new version; one with a carbon-fiber casing, instead of the current metal one. The new version would create fewer dangerous fragments, when it explodes. Why crate a less effective bomb? Because in urban areas, you often want to just do damage to a building or bunker, and not to any nearby civilians. The SDB is designed to penetrate concrete and earth, depending on the setting of its fuze. Normally, an SDB destroys a building, in which case the structural debris is also dangerous to nearby civilians, while fragments from the SDB are contained within the building. But, just to be on the safe side, the carbon-fiber casing version will be developed, and should be ready for action in about two years.

The metal case 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 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. It's shape is more like that of a missile than a bomb (70 inches long, 190 millimeters in diameter), with the guidance system built in. The smaller blast from the SDB was meant to result in fewer civilian casualties when used in an urban area. 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, smaller, GPS bombs available. This caused the 500 pound JDAM to get developed quickly and put into service.

The air force wants to equip the B-1 with SDBs, as this bomber could carry as many as 216 of them. The new F-22 and F-35 warplanes are stealthy and normally carry their bombs internally. This limits how many they can carry, but with the SDB, an F-22 can carry eight of them. The Navy F-18 could easily carry 24 SDBs. The SDBs are carried on a special carriage, which holds four of them. The carriage is mounted on a bomber just like a single larger (500, 1,000 or 2,000) pound bomb would be.

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 each.) JDAM (a guidance kit attached to a dumb bomb) only cost about $26,000. The small wings allow the SDB to glide up to 70-80 kilometers (from high altitude.) SDB also has a hard front end that can punch through several feet of rock or concrete, and a warhead that does more damage than the usual dumb bomb (explosives in a metal casing.) The SDB is thus the next generation of smart bombs.

There have been 250 pound dumb bombs, but these days, such a bomb is too inaccurate to be useful. It also made sense to merge the guidance kit and the bomb itself. The superiority of guided bombs is such that the next generation of heavier (500-2000 pound) smart bombs will probably be like the SDB.

The official name of the SDB is now "Focused Lethality Munitions," but that's another story.