46 people on the Italian ship perished, five on the Stockholm

Nearly six decades after the luxury liner Andrea Doria sank off the coast of Nantucket, Massachusetts, killing dozens, explorers are preparing an underwater mission to the wreckage.

A Washington state-based ocean exploration company is planning the first manned submersible expedition to the wreck in 20 years.

Everett, Washington-based OceanGate will use its five-man submersible Cyclops I next month to get high-definition video and 3-D sonar images of the shipwreck, technology never before used to study the famous maritime disaster.

Nearly six decades after the Andrea Doria (pictured in July 1956) slammed into another ocean liner, killing 46 people, explorers are preparing a mission to get a fresh glimpse of the wreckage on the sea floor

Everett, Washington-based OceanGate will use its five-man submersible Cyclops I next month to get high-definition video and 3-D sonar images of the shipwreck

The plan is to do two three-hour dives per day during the weeklong expedition. The June mission is to document and observe, not collect artifacts

'The Andrea Doria stands out as the premier shipwreck in American waters,' said Stockton Rush, the company's co-founder and chief executive officer.

The New York-bound Italian luxury liner sank after a collision on the foggy night of July 25, 1956, with the Swedish ship Stockholm, which was heading back to Europe.

The Stockholm ripped a gash in the Andrea Doria's hull, causing it to list and making some of its lifeboats unusable. Five people on the Stockholm died, but 46 crew and passengers on the Italian ship perished. More than 1,600 others were rescued as the ship took 11 hours to sink.

The wreck, in about 240 feet of water 50 miles south of Nantucket, has for years attracted treasure-hunting divers looking for money, china and other artifacts from a bygone era. But 16 of those divers have died, the most recent just last year.

The wreck has been compared to Mount Everest, because it is as alluring and dangerous to divers as the world's tallest peak is to mountaineers.

Stranded: The Andrea Doria lists heavily after being hit by the Stockholm on July 26, 1956. Note the lifeboats on the port side which could not be lowered and used because of the list to starboard

Survived: An aerial view of the Stockholm entering harbor after crashing with Andrea Doria; Stockholm's bow was repaired at a cost of $1million and today it sails as the MV Astoria under a Portuguese flag

The Andrea Doria (pictured 1948 leaving New York) has for years attracted treasure-hunting divers looking for money, china and other artifacts from a bygone era. But 16 of those divers have died, including one last year

'A big part of the danger is the depth and the risk of nitrogen narcosis,' said OceanGate marketing director Joel Perry, a condition in which too much nitrogen builds up in the blood, clouding judgment.

Visibility at that depth is poor, currents are unpredictable and plenty of protrusions can snag a diver, he said.

Because of its depth, divers can only spend about 20 minutes exploring the wreck. The Cyclops I, with an interior about the size of a Chevrolet Suburban, can stay down for hours.

Luxury in a bygone era: The Andrea Doria's dining room is seen in this 1955 file photograph

Captain on deck: People are seen inside the Andrea Doria's helm in this file photograph

The plan is to do two three-hour dives per day during the weeklong expedition. The June 2-9 mission is to document and observe, not collect artifacts.

It's being conducted with the help of Boston Harbor Cruises, which is providing the operational vessel, and iXBlue, which is providing navigation services.

'The Andrea Doria is rapidly decaying, and using this technology we can build a 3-D map of the wreck with very high accuracy that scientists can use to compare with future decay,' Rush said.

The findings, in turn, could be applied in studies of other shipwrecks.