The discovery of the ozone ‘hole’ in 1985 in the Antarctic came as a shock not only to the informed public but also to the scientists. The losses of ozone were very high at all levels of the stratosphere and no theory or mathematical model then known could explain the extent of the ozone loss. The scientists then attempted explanations. Some ascribed it to CFCs and others to atmospheric dynamics. A resolution of the debate clearly required further observations to validate any of the theories. An expedition mounted to the US Antarctic station in McMurdo in August 1986 could not resolve the debate. Scientists including Crutzen and Molina then proposed new theories, which subsequently proved right but still required validation by observation. A second, larger expedition was then led in August 1987 by NASA with aircraft reaching the ‘ozone hole’ for observations. These observations, along with the ground observations, provided the ‘smoking gun’ to implicate the CFCs prominently in the ozone depletion. Scientists found that ozone in the stratosphere was less when the chemical chlorine monoxide was high and vice versa. Chlorine monoxide was formed in the process of catalytic destruction of ozone by CFCs and had no other natural source. This convinced the scientists that the atmospheric dynamics, which some blamed for the ozone depletion, only set up the conditions to promote ozone destruction by CFCs. The CFCs were the main villains. These results came in slightly after the diplomatic conference in Montreal that arrived at the Montreal Protocol and had no effect on the diplomats who negotiated the Protocol. The Montreal Protocol, as a result, prescribed only mild controls on CFCs and halons.