Yes, the Johnston Atoll housed a chemical weapons depot and the site of the Johnston Atoll Chemical Agent Disposal System (JACADS). All of the chemical weapons that were once stored on Johnston Island have been incinerated, and that process was completed in 2000 and JACADS demolished by 2003. The base was closed and the airport deactivated on June 15, 2004.
Some people think, that abandoned bases like the one on the Johnston Atoll and also the Michael Army Airfield (MAAF) at Dugway Proving Ground, Utah are the new "Area 51" / Dreamland", where new secret aircrafts like the "Aurora" are/ have been tested.