Under an August 2 contract worth $32 million, the aerospace firm Boeing is due to produce eight of the giant MOP bombs to fulfil the air force's "operational needs" , according to Miller.The air force could not say how many of the conventional bombs have been delivered so far, but the MOP is seen as a weapon made for going after underground bunkers and tunnels in North Korea or Iran. With more than 5,000 pounds of explosives, it is supposed to fit on a B-2 stealth bomber to strike at underground sites hiding weapons of mass destruction.About six meters long, the GPS-guided bomb "will defeat our adversaries' WMD before they leave the ground" , according to an official description posted on the website of the defence threat reduction agency and US strategic command.The United States, which suspects Iran and North Korea have built nuclear facilities deep underground to thwart any possible air raids, has been developing the MOP bomb since about 2007. The bomb is made to penetrate up to 200 feet of reinforced concrete before exploding.