During the annual tour in 1975, a second plaque was added below the first by The National Park Service, designating Trinity Site a National Historic Landmark. This plaque reads, "This site possesses national significance in commemorating the history of the U.S.A." JUMBO Lying next to the entrance of the chain link fence that still surrounds Trinity Site are the rusty remains of Jumbo. Jumbo was the code name for the 214-ton Thermos shaped steel and concrete container designed to hold the precious plutonium core of the Trinity device in case of a nuclear mis-fire. Built by the Babcock and Wilcox Company of Barberton, Ohio, Jumbo was 28 feet long, 12 feet, 8 inches in diameter, and with steel walls up to 16 inches thick. The idea of using some kind of container for the Trinity device was based on the fact that plutonium was extremely expensive and very difficult to produce. So, much thought went into a way of containing the 15 lb. plutonium core of the bomb, in case the 5,300 lbs. of conventional high explosives surrounding the core exploded without setting off a nuclear blast, and in the process scattering the costly plutonium (about 250 million dollars worth) across the dessert. After extensive research and testing of other potential containment ideas, the concept of Jumbo was decided on in the late summer of 1944. However, by the spring of 1945, after Jumbo had already been built and transported (with great difficulty) to the Trinity Site by the Eichleay Corporation of Pittsburgh, it was decided not to explode the Trinity device inside of Jumbo after all. There were several reasons for this new decision: first, plutonium had become more readily (relatively) available; second, the Project scientists decided that the Trinity device would probably work as planned; and last, the scientists realized that if Jumbo were used it would adversely affect the test results, and add 214 tons of highly radioactive material to the atmosphere. Not knowing what else to do with the massive 12 million dollar Jumbo, it was decided to suspend it from a steel tower 800 yards from Ground Zero to see how it would withstand the Trinity test. Jumbo survived the approximately 20 kiloton Trinity blast undamaged, but its supporting 70-foot tall steel tower was flattened.