Israel has developed a new 500 pound (227 kg) penetrator bomb, the MPR-500. The MPR-500 can smash through more than a meter (39 inches) of concrete or four 200mm (8 inch) concrete barriers (floors or bunker walls) and then detonate. When the MPR-500 explodes it releases 26,000 fragments, which will wound or kill out to 100 meters.
While the MPR-500 is an unguided bomb it is most useful when mated with a guidance kit to become a smart bomb. The most common such kit is the American JDAM, which converts 500, 1,000 (455 kg) and 2,000 (910 kg) pound unguided bombs into highly accurate guided "smart bombs."
Currently, most penetrator bombs are heavier (910 kg) and models like the BLU-109 can penetrate five meters (16 feet) of concrete. The heavier (5,000 pound) GBU-28 can penetrate 32 meters (100 feet) of earth or six meters (20 feet) of concrete. Israel already has hundreds of these larger penetrator bombs but apparently sees a need for smaller penetrators. More of the smaller bombs can be carried on each sortie. There are smaller penetrators as well.
Israel had watched (from the air and via spies on the ground) as the Iranian supported Hezbollah militia built underground bunkers in southern Lebanon over the last twelve years. Hezbollah built many of these bunkers into homes and schools. Others were dug into mountains. While there were a lot of targets that required the GBU-24 and 28, there were many more that could be destroyed with smaller bombs. For some of those Israel has bought thousands of 250 pound (114 kg) American Small Diameter Bombs (SDB), which can penetrate half a meter (20 inches) of rock or concrete and much more packed earth. With the addition of the locally made MPR-500 Israel has a penetrator for every buried target.
