North Pacific Ocean atoll, about a third of the way between Hawaii and the Marshall Islands. A U.S. Territory.
Johnston Atoll Chemical Agent Disposal System (JACADS). Former U.S. nuclear weapon test site.
Sand Island is only about 1 mile northeast.
Although part of the U.S. National Wildlife Refuge System, and partially administered by Fish and Wildlife Service of the Department of the Interior, it is closed to the public: you have to be military or a military contractor to go there.
The other part of the Johnston Island management team is the Defense Threat Reduction Agency (DTRA).