The BLU-113 bunker buster bomb, designed and built in 17 days during the 1991 Gulf War, is designed to penetrate more than 20 ft of reinforced concrete or 100 ft of earth before detonating 675 pounds of Tritonal explosive inside a bunker. The BLU-113 is usually fitted with a laser guidance kit, turning it into the GBU-28, a 19 foot long, 4700 pound weapon. Saddam Hussein is known to have built two heavily protected underground shelters in 1982 and 1983. The German firms that designed and constructed these 20,000 square foot shelters described them as having 7 feet of reinforced concrete for a ceiling and walls of five feet of reinforced concrete. The main entrance is through a three ton steel door. There are two escape tunnels, one going 200 meters to the Tigris river. One bunker is under a Presidential Palace, which would have to be leveled before the GBU-28 could get a shot at the bunker several dozen feet underneath.