The prehistory of Google Earth began in 2001 when a software development firm called Keyhole, Inc., was founded in Mountain View, California, which happened also to be Google's base of operations. Keyhole specialized in geospatial data visualization applications. The name "Keyhole" paid homage to the original KH reconnaissance satellites, also known as Corona satellites, which were operated by the U.S. between 1959 and 1972. Google acquired Keyhole in 2004, and Keyhole's Earth Viewer reached a wide public as Google Earth in 2005. Other aspects of Keyhole technology were incorporated into Google Maps.