The USS Tripoli (LPH-10), shown above in then-and-now views, is a former US Navy amphibious assault ship that was commissioned in 1966.
Built to serve primarily as a helicopter landing pad and floating Marine barracks, the Tripoli earned nine campaign stars in the Vietnam War. On February 18, 1991, during the Gulf War, the Tripoli hit a mine while sailing off the coast of Iraq. The blast ripped a 16-foot hole below the waterline, but after extensive repairs, the ship returned to duty, and later sailed to Somalia in 1992 to land Marines in Mogadishu as part of Operation Restore Hope.
After a busy career, the Tripoli was decomissioned in 1995 at the Mare Island Naval Shipyard in Vallejo, California, where it has remained -- in a state of graceful decay -- ever since. Ownership of the vessel was transferred to the Army in 1997, and in 2001, strange, tent-like structures appeared on her decks. Telstar Logistics managed to get aboard once, briefly, in 2002 although we opted to depart before learning more about the work that was underway —and before our luck ran out.
While driving across the Golden Gate Bridge on August 27, 2006, one of our spotters noticed the Tripoli being towed out to sea. After pulling over to the scenic overlook, a quarter was depoited into a pair of tourist binoculars, and more detailed intelligence was acquired. The tent-like structures had been relocated, and two very large trailer-mounted satellite antennas were visible on the flight deck. Hmmmmmmm...
Further research revealed that the Tripoli has again been drafted into service. In its second career, the ship is being used as a Mobile Launch Platform for the development of the Pentagon's missile defense program:

The Mobile Launch Platform uses the former USS Tripoli as its launch platform. It is being utilized to provide the ability to present threat azimuth diversity for [ballistic missile defense system] element tests, and it provides the ability to place Surface Sensors in remote ocean areas.
Recent accomplishments for the MLP are successfully Launching 2 Lance Missiles from the deck, completed Operational and Maintenance Modifications, and developed site plan for the Transportable Telemetry System (TTS).
And sure enough, a few days after the Tripoli was towed out the Golden Gate, the military announced the successful completion of a missile intercept test.
Last week, the Tripoli reappeared. Now tied up in at Pier 80 on San Francisco's southern waterfront (below), teams of workers could be seen coming and going from the gangway, but the the exact nature of their efforts remains unknown. What's next for the Tripoli? That's unknown as well, although if the recent past is any guide, the ship is not likely to spend the remainder of her retirement playing shuffleboard, mahjongg, or bingo.

Historical photos from Steve Stengel a former electronics technician aboard USS Tripoli from 1984-1986: LINK