None of them are anywhere near as cool as Deep Digger, the bunker-busting bomb that drills its way underground. But various arms of the Defense Department are working on a number of next-generation munitions, designed to take out deeply buried targets, Aviation Week writes.<br/><br/>With 5,300 lb. of explosive material, MOP will pack more than 10 times the explosive punch of its BLU-109 [today's bunker-busting workhorse] predecessor... Optimum penetrating distance is classified, but some analysts say it is as much as 200 ft. through reinforced concrete and soil or sand...<br/><br/>MOP will have a blunter nose than its predecessors to keep the weapon intact during penetration... The majority of MOP's weight is actually carried in the heavy steel casing, according to AFRL [Air Force Research Lab] officials. Once the tests are finished next year, the Pentagon will decide whether to produce the MOP and begin a small stockpile...<br/><br/>About six years ago, AFRL officials developed the Advanced Unitary Penetrator (AUP), which can burrow twice the depth of the BLU-109. The weapon uses denser materials "to pack more mass into a smaller cross-section," Sands says. It is essentially a massive explosive bullet encased in a shroud that is dimensionally the same as the BLU-109. During penetration, the outer casing peals off, leaving the core to dig and detonate. The technology has been proven but has not been purchased by the Air Force, quite possibly because they need to go deeper still.<br/><br/>Thus, engineers have been experimenting with various steel formulations to improve the likelihood that a penetrator will survive on its path to a target without breaking up midcourse.<br/><br/>Through years of work, AAC and Ellwood National Forge in Irvine, Pa., have developed a very strong steel that is being used on the BLU-122, the Air Force's newest penetrator, weighing in at 5,000 lb. The team has applied for a patent for the chemical composition and manufacturing process that has produced "Eglin Steel," a strong blend estimated at one-eighth the cost of experimental metals with similar strength. Prior attempts to formulate similar steel have proved cost prohibitive. The patent for Eglin Steel -- a blend of carbon, chromium and tungsten for hardness, and of silicon and nickel for durability -- is under final review.