The hulking wreck has been a regular destination for divers but a riddle to historians: What ship came to rest in 85 feet of water 10 miles off New Jersey's coastline?

Now, federal officials have an answer.

The National Oceanic and Atmospheric Administration announced Tuesday that it has confirmed that the ship is the Robert J. Walker, an iron-hulled steamer doing mapping work for the U.S. Coast Survey that sank 153 years ago after a violent collision with a 250-ton schooner.

Twenty sailors aboard the Walker died, making it the worst accident in the history of the U.S. Coast Survey or its successor, the National Oceanic and Atmospheric Administration.

The wreck was discovered by fishermen in the 1970s but its identity was a mystery until June when a NOAA ship conducting surveys for navigation safety in the aftermath of Superstorm Sandy made a positive identification. Retired NOAA Capt. Albert Theberge and Joyce Steinmetz, a Ph.D. candidate in maritime archaeology at East Carolina University, provided impetus for the project.

"It's estimated there are 3 million shipwrecks in the waters of the world," said James Delgado, director of maritime heritage for NOAA's office of national marine sanctuaries. "You can't go out and look for every one, but sometimes the situation arises when you have an opportunity to do that. This was a perfect convergence of opportunity."

Delgado said the Walker could be one of the last remaining shipwrecks to be identified off the New Jersey coast. According to NOAA, the ship's unique engines and rectangular portholes were key identifying features. It was still pointed toward Absecon lighthouse, where it likely was trying to head before it sank.

Built in 1847, the Walker did survey work charting the waters of the southern United States and contributed to the opening up of many ports on the Gulf Coast to increased commerce, according to NOAA. Its work also helped chart harbors that would become strategically important for the Union Navy in the looming Civil War.

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On the night of June 21, 1860, the Walker was heading north to New York when it collided with the schooner Fanny, headed from Philadelphia to Boston. In a newspaper interview, the ship's quartermaster described the scene as the steamer sank within about 30 minutes.

"The men stayed by the steamer until she was sinking, and then, without confusion, such of them as could took to the boats," Charles Clifford told the New York Herald. "Many of the crew went down with the steamer, however, clinging to the spars and portions of the wreck. ... The captain stayed on board until the steamer went down, and just before she disappeared from sight jumped into the water, and was picked up by one of the boats."

Perhaps due to the approaching Civil War, the U.S. Coast Survey didn't conduct an inquiry into the cause of the collision or assign responsibility, NOAA notes.

Delgado said the wreck won't be raised, and said he hopes it can be used as a tool for educating the public on shipwrecks and creating interest in diving.