SUNNYVALE, Calif. -- A top secret military installation closed Wednesday after 50 years as a Bay Area landmark. The "Blue Cube" on Onizuka Air Station was once rumored to be one of the highest-ranking nuclear targets in the United States.

Thousands of drivers saw the building as they drove through Sunnyvale on Highways 101 or 237. But few knew the building was the home to a dedicated team who monitored and controlled spy satellites.

The nine-story tall windowless building actually has only four floors. It also contains miles and miles of cables and wires hooked to computers.

At one time, 5,000 people worked there. But economics and new technology brought about the demise of this facility but there are good memories.

Operations are being moved to Vandenburg Air Force Base In Southern California. The City of Sunnyvale may allow auto dealers to occupy the property.

The facility started out as Sunnyvale Air Station, but was renamed for Astronaut Ellison Onizuka, who trained there and was later killed in the Space Shuttle Challenger explosion.