This is a museum quality reproduction of a very rare pin that was awarded to project members who spent over one year working on the Mahattan Project. The pin is ¾ of an inch in diameter as was the original and in sterling silver. A bronze pin was awarded to those who worked less than a year on the effort. The Manhattan Project was the effort which led to the development of the atomic bomb by the US during WW-II. Though the eventual use of the bomb on Hiroshima and Nagasaki remains a subject of controversy some 60 years later, there is little doubt that the number of casualties on both sides would have been far greater if an invasion of the Japanese home islands had actually been necessary.