March 5,2008: The U.S. Air Force is spending $1.2 billion on development and production of its SDB (small diameter bomb). A thousand of the SDBs have been produced, and another 23,000 are on the way over the next seven years. In addition, 2,000 special racks for all U.S. Air Force bombers, are in production. The SDB entered mass production two years ago, and over a hundred have been used in the last year.

The SDB is basically a second generation JDAM smart (GPS guided) bomb design. The basic JDAM arrived in 2001, but came in only two sizes; half ton and one ton. This was too much blast for urban fighting. The need for less firepower compelled the air force to quickly modify its GPS guidance kit to fit on a 500 pound bomb. But that's still 280 pounds of explosives. The troops wanted precision, and less bang. In response, the air force (actually, the navy) developed a 500 pound bomb with all but 30 pounds of the explosives removed. Then came a completely new smart bomb design, the 250 pound SDB (small diameter bomb). This weapon has a shape that's 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 is still pretty substantial (51 pounds of explosives). This soon led to a SDB variant, with the Focused Lethality Munition (FLM) warhead, which reduces the number of metal fragments created when the bomb explodes, and increases the blast effect. This is meant to reduce casualties to nearby civilians, but it's still a bigger bang than the low-explosive 500 pound JDAM. Moreover, the low-explosive JDAM costs about half as much as the SDB. The one advantage of the SDB is that you can carry more of them, as they are much more compact than 500 pound bombs. Still, increased competition from GPS guided rockets and artillery shells has reduced the need for any kind of JDAM. So while the air force has more, and better, bombs, it is called on less to use them.