Johnston Atoll

Both the US and the Kingdom of Hawaii annexed Johnston Atoll in 1858, but it was the US that mined the guano deposits until the late 1880s. Johnston Island and Sand Island were designated wildlife refuges in 1926. The US Navy took over the atoll in 1934, and subsequently the US Air Force assumed control in 1948. The site was used for high-altitude nuclear tests in the 1950s and 1960s, and until late in 2000 the atoll was maintained as a storage and disposal site for chemical weapons. Cleanup and closure of the weapons facility ended in May 2005.
Source: World Factbook 2020