At the peak of the Atomic Age, the United States initiated Operation Plowshare, involving "peaceful nuclear explosions". The United States Atomic Energy Commission chairman announced that the Plowshare project was intended to "highlight the peaceful applications of nuclear explosive devices and thereby create a climate of world opinion that is more favorable to weapons development and tests". The Operation Plowshare program included 27 nuclear tests designed towards investigating these non-weapon uses from 1961 through 1973. Due to the inability of the U.S. physicists to reduce the fission fraction of low-yield (approximately 1 kiloton) nuclear devices that would have been required for many civil engineering projects, when long-term health and clean-up costs from fission products were included in the cost, there was virtually no economic advantage over conventional explosives except for potentially the very largest projects.