The U.S. Air Force is spending $36 million to develop a new Hard Target Sensing Fuze for its 1-2.5 ton penetrator bombs. The new fuze will be reprogrammable by the pilot, while in the air. The pilot can specify how deep the bomb should go before detonating, as well as how many voids (levels of an underground bunker) to go through before detonating. A time delay can also be specified. The new fuze must be able to survive a penetration force of 15,000 pounds per square inch (one ton per square cm). The new fuze will be used with the BLU-109, 113 or 122 bombs. Increasingly, over the last decade, the air force has become more interested in larger non-nuclear bombs, and especially penetrating bombs.
Two years ago, the air force asked Congress for money to buy up to a dozen 15 ton Massive Ordnance Penetrator (MOP) bombs. The likely targets were North Korea or Iran, and apparently the air force had developed some new information on targets that would require more MOPs, and as soon as possible.
The U.S. Air Force also modified some B-2 bombers so that they could carry two MOP bombs. These 7 meter (21 foot) long bombs had begun development in 2004, with the first test models showing up in 2005. Operational characteristics (how deep the bomb can go in different types of material) have only mentioned the ability to penetrate 65 meters (200 feet) underground. The MOP is mostly metal, with about 18 percent of its weight devoted to explosives. It uses GPS, and inertial guidance, to find its target. The MOP is the latest of a long line of American "super bombs." B-2s are supposed to be ready to use MOP next year. Previously, the heaviest U.S. "penetrator" bombs were the 2.1 ton BLU-28 and one ton BLU-109.
MOP is not the first U.S. "super bomb." In 2003, the U.S. put into service the nine ton MOAB (Massive Ordnance Air Blast), but this has never been used in combat. MOAB is pushed out the back of a SOCOM (Special Operations Command) MC-130E aircraft. The blast can be felt several kilometers away, and the mushroom shaped cloud (that rises to over 3,200 meters/10,000 feet) can be seen more than 40 kilometers away.
MOAB replaced the Vietnam era BLU-82 (Daisy Cutter ) bomb, which used a 6.3 ton slurry of ammonium nitrate and powdered aluminum. MOAB uses more powerful tritonal explosives. In addition to a more powerful explosion, MOAB doesn't need a parachute, like the Daisy Cutter, but uses a GPS (like JDAM) and an aerodynamic body to detonate the bomb at a precise area. Thus the MOAB can be dropped from a higher altitude (like outside the range of machine-guns and rifles).
MOAB can also be shoved out the back of a cargo aircraft (usually a C-130, but since the MOAB uses GPS and higher altitude drops, the C-17 can probably be used as well.) MOAB is a highly destructive and terrifying weapon. If used in combat, the force of a MOAB explosion is sufficient to knock over tanks and kill any people within several hundred meters of the detonation.
Russia has also built a bomb similar to MOAB, but theirs contains 7.1 tons of a more powerful explosive than MOAB or MOB used, and that the blast radius of the Russia bomb is 300 meters, which is twice the size of MOAB, and larger than MOB. While MOAB is equivalent to 11 tons of TNT (the benchmark for measuring different explosives), the Russian bomb was said to be equal to 44 tons of TNT. It also appeared, from the Russian test video, that their bomb was a FAE (fuel air explosive). This could be seen from the typical FAE two stage explosion. A Russian video also showed the area surrounding the blast, and the damage was consistent with an FAE explosion, and about as powerful as MOAB. It appears that the Russians were making publicity, not a factual announcement of a new weapon.
Penetrator bombs are more high-tech than the "big bang" bombs like MOAB. There's a lot of calculations required, and attention to which materials are used and how they are put together. But if your opponent likes to bury things underground, a large penetrator bomb is just the kind of nightmare you want to have handy.