During WW2 the British developed the Tallboy and Grandslam bombs to destroy German reinforced concrete sub-pens and other large concrete targets. For the most part they were partially successful (against the V-3 site but not so much with the sub-pens). During the Second Gulf War (OIF), however, the German engineer of Saddam's underground Q4 bunker told the coalition that nothing they had in inventory nor sheer numbers of bunker-busters would scratch his design. It was hit with 80 tons of ordnance and bunker-busters and failed miserably against the joint German/Yugoslav design work with Swiss reinforced blast doors. So in the years afterwards there was a drive for a giant GBU by Norhtrop that got stalled and now has been re-designed by Boeing as the MOP (Massive Ordnance Penetrator) of 30,000 lbs with precision GPS guidance. It can penetrate 200 feet against moderate reinforced concrete, but only 26 ft of heavily reinforced concrete or 130 ft of solid rock. Impressive in inventory, however, this still would not penetrate the German Q4 bunker!!! And for further info the first bunker-buster was the WW2 German Rochling AC shell made of vanadium and chromium. It was stored after tests against the Maginot Line and other Belgian targets. Since Germany had the most concrete fortifications, it was feared that a captured example might be duplicated, so Hitler had them stored for the duration of the war (with only slight testing in Russia too). The USAF hopes to arm most of the B-2 fleet, but Northrop must modify the bays to carry these weapons and it is also to be carried by the enigmatic B-3 design suggesting that possibly Boeing or Northrop already have a design in development (no mention of Lockheed)...

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