May 15, 2007: The U.S. Navy wanted a smart bomb that did not pack as much punch as the smallest one currently available, the 500 pounder. Rather than buy the expensive (over $50,000 each) air force 250 pound SDB (Small Diameter Bomb), the navy simply had some 500 pound bombs modified to remove about half the explosives. Thus they get the same bomb explosive performance as the SDB, at half the cost. The SDB, of course, is designed to penetrate concrete or ground, as well as being much smaller than the 500 pound bomb. That's all well and good, but all the navy wanted was a bomb that was safer to use against targets in urban areas, where there are a lot of civilians about.