August 30, 2011: Russia recently introduced its newest, and smallest, smart bomb. The KAB-250 is a 250 kg (550 pound) smart bomb. Not a kit to be added to a dumb bomb, the KAB-250 is a compact, 255mm (10 inch) diameter, 3.2 meter (9.9 foot) long TV guided bomb. It is compact enough for internal bomb bays increasingly found in fighter-bombers (to increase stealthiness) or for allowing more bombs to be carried suspended under the wings. The KAB-250 is following the lead of the U.S. Air Force Small Diameter Bomb (SDB, also known as the GBU-39/B). But there are several features the SDB has, which have not yet been added to the KAB-250

The SDB weighs 130 kg (285 pound) and costs about $70,000 each. That is, it is lighter, and more expensive than the KAB-250. Like the KAB-250, the SDB was designed from the bottom up as a smart bomb. It was only five years ago that the U.S. 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 smaller (227 kg/500) pound JDAM (GPS guided bomb kit).

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. Its shape is more like that of a missile than a bomb (nearly two meters, as in 70 inches, long, and 190 millimeters in diameter), with the guidance system built in. The smaller blast from the 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, smaller, GPS bombs available. This caused the 227 kg (500 pound) JDAM to get developed quickly and put into service. But it wasn't small enough for many urban combat situations. The SDB carries only 17 kg (38) pounds of explosives, compared to 127 kg (280) pounds in the 500 pound bomb and the KAB-250.

The SDB is basically an unpowered missile, which can glide long distances. This makes the SDB even more compact, capable and expensive. 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.) KAB-250 also uses small wings to give it some range, but not as much as the SDB.

SDB also has a hard front end that can punch through more than two meters (eight 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. The more compact design of the SDB 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 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 U.S. Air Force is developing SDB II (GBU 53), which will include an encrypted data link that enables the SDB to hit moving targets. This communications capability enables the SDB movement to be controlled via the air force's airborne Internet (Link 16). This capability is one of the main improvements to be seen in SDB 2, which won’t enter service for another few years.

Meanwhile, there are numerous tweaks being made to the software of the original SDB. For example, one of these changes enabled SDBs to be used like a JDAM (GPS guided bomb). That is, it can now, with the new software, be dropped from an aircraft while directly above the target. The SDB was built as a glide bomb, which was dropped ten or more kilometers from the target, then glided for a bit 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. Another software change has made SDBs get to the target faster.