The National Science Foundation (NSF) announced on Friday that the Alvin deep-sea submersible is returning to service. The DC3 of the oceanographic world was launched fifty years ago in 1964 and is ready to begin its second half-century of service after a three-year overhaul involving significant redesigns and upgrades.

Owned by the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI) for the National Deep Submergence Facility on behalf of a consortium of universities and research organizations, Alvin has been out of service since December 2010 while undergoing a major overhaul. According to the NSF, the upgrades included replacement of its personnel sphere with a larger one providing better ergonomics, five view ports to replace the three in the old sphere, as well as an improved depth rating of 6,500 m (21,000 ft). There's also new lighting, a high definition imaging system, and better command and control systems.

On completion of the upgrades, the Naval Sea Systems Command (NAVSEA) used its Deep Submergence Scope of Certification process to certify that Alvin could safely operate at a depth of 3,800 m (12,000 ft) as part of Stage I of the sub's upgrade. This is the same review process used by the Navy to certify submarine rescue craft and submersibles used by Special Operation Forces and involved weeks of testing Alvin on increasingly deep dives off San Diego.

Later this year, Alvin will undertake another series of dives to certify it to a depth of 4,500 m (15,000 ft). In the meantime, beginning in March, the submersible will carry out a "science verification" cruise followed by three research expeditions to the Gulf of Mexico to study the impact of the Deep Horizon oil spill, to the Juan De Fuca Ridge, and the East Pacific Rise and Dorado Outcrop off Costa Rica.

"The modifications made to Alvin during this upgrade and overhaul have exponentially improved its capabilities," says Pat Hickey, Alvin manager and one of the chief test pilots. "The new LED lights save power while illuminating a far greater area than before, and the bigger and repositioned windows improve visibility. By repositioning the manipulators, we increased our work area, and the larger science basket allows us to load up to 400 pounds (180 kg) of exterior equipment and samples. An additional lateral thruster now allows the sub to hover like an underwater helicopter."

Commissioned in 1964, Alvin reaches its 50th year of service this year. Over its life, the deep-ocean submersible has clocked up over 4,600 dives, including locating a lost hydrogen bomb in the Mediterranean Sea in 1966, exploring the first known hydrothermal vent sites in the 1970s, and surveying the wreck of the Titanic in 1986. Its latest overhaul will ensure Alvin will continue to enable new discoveries in deep-sea geology, chemistry and biology for many years to come.

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