The Da Vinci Research Base was a top-secret American laboratory in Antarctica, with a focus on adjustments in Earth's ozone layer and funded covertly by the United States Defense Department through the Environmental Protection Agency and National Institute of Science.
In 1984, Wilson Evergreen was a scientist working at this lab when Guinan informed Gary Seven of the base's existence and the research they were doing. This led Seven to undertake a mission with a young Khan Noonien Singh in order to stop the research which would allow for the control of Earth's ozone layer as a dangerous weapon. After Seven showed Evergreen that his research was being funded by the Defense Department he agreed to destroy the base and allow the hole in the ozone to remain as a warning to Earth's inhabitants. Shortly after they stood by and watched the base blow up. (TOS novel: The Rise and Fall of Khan Noonien Singh, Volume 1)