Potential stratospheric ozone perturbations following a nuclear war would be highly dependent on the yield of the individual explosions. The senario involving mainly high-yield nuclear weapons described in Vol. I yields a maximum ozone column depletion of 44% after 6 months. Scenarios involving lower yield weapons would produce little stratospheric ozone reduction. As calculated with simple one-dimensional models assuming an unperturbed climate, maximum ozone depletion would be reached in 6-12 months, and a depletion of at least 10% could persist for about 3 to 6 years for the high-yield scenario. The effectively instantaneous meridional and longitudinal spreading that occurs in the one-dimensional model utilized in these calculations may under-estimate ozone reduction in the Northern mid-latitudes for the first few months, when the injected NOx would remain peaked over the involved areas. Increases in ultraviolet flux at the surface would depend on latitude and season, and absorption by intervening clouds of smoke and other species.