SAVANNAH, Ga. (AP) — Before government engineers can deepen one of the nation's busiest seaports to accommodate future trade, they first need to remove a $14 million obstacle from the past — a Confederate warship rotting on the Savannah River bottom for nearly 150 years.

Confederate troops scuttled the ironclad CSS Georgia to prevent its capture by Gen. William T. Sherman when his Union troops took Savannah in December 1864. It's been on the river bottom ever since.

Now, the Civil War shipwreck sits in the way of a government agency's $653 million plan to deepen the waterway that links the nation's fourth-busiest container port to the Atlantic Ocean. The ship's remains are considered so historically significant that dredging the river is prohibited within 50 feet of the wreckage.

So the Army Corps of Engineers plans to raise and preserve what's left of the CSS Georgia. The agency's final report on the project last month estimated the cost to taxpayers at $14 million. The work could start next year on what's sure to be a painstaking effort.

And leaving the shipwreck in place is not an option: Officials say the harbor must be deepened to accommodate supersize cargo ships coming through an expanded Panama Canal in 2014 — ships that will bring valuable revenue to the state and would otherwise go to other ports.

Underwater surveys show two large chunks of the ship's iron-armored siding have survived, the largest being 68 feet long and 24 feet tall. Raising them intact will be a priority. Researchers also spotted three cannons on the riverbed, an intact propeller and other pieces of the warship's steam engines. And there's smaller debris scattered across the site that could yield unexpected treasures, requiring careful sifting beneath 40 feet of water.

"We don't really have an idea of what's in the debris field," said Julie Morgan, a government archaeologist with the Army Corps. "There could be some personal items. People left the ship in a big hurry. Who's to say what was on board when the Georgia went down."

Also likely to slow the job: finding and gently removing cannonballs and other explosive projectiles that, according to Army Corps experts, could still potentially detonate.

That's a massive effort for a warship that went down in Civil War history as an ironclad flop.

The Civil War ushered in the era of armored warships. In Savannah, a Ladies Gunboat Association raised $115,000 to build such a ship to protect the city. The 120-foot-long CSS Georgia had armor forged from railroad iron, but its engines proved too weak to propel the ship's 1,200-ton frame against river currents. The ship was anchored on the riverside at Fort Jackson as a floating gun battery.

Ultimately the Georgia was scuttled by its own crew without having ever fired a shot in combat.

"I would say it was an utter failure," said Ken Johnston, executive director of the National Civil War Naval Museum in Columbus, Ga., who says the shipwreck nonetheless has great historical value. "It has very clearly become a symbol for why things went wrong for the Confederate naval effort."

As a homespun war machine assembled by workers who likely had never built a ship before, the CSS Georgia represents the South's lack of an industrial base, Johnston said. The North, by contrast, was teeming with both factories and laborers skilled at shipbuilding. They churned out a superior naval fleet that enabled the Union to successfully cut off waterways used to supply Confederate forces.

Despite its functional failures, the shipwreck's historical significance was cemented in 1987 when it won a place on the National Register of Historic Places, the official listing of treasured sites and buildings from America's past. That gave the Georgia a measure of protection — dredging near the shipwreck was prohibited.

Still, a great deal of damage had already been done. The last detailed survey of the ship in 2003 found it in pieces and its hull apparently disintegrated. Erosion had taken a large toll, and telltale marks showed dredging machinery had already chewed into the wreckage.

Salvaging the remains will likely move slowly.

Divers will need to divide the site into a grid to search for artifacts and record the locations of what they find. The large sections or armored siding will likely need to be cradled gently by a web of metal beams to raise them to the surface intact, said Gordon Watts, an underwater archaeologist who helped lead the 2003 survey of the shipwreck.

The Army Corps' report also notes special care will be needed find and dispose of any cannonballs and other explosive projectiles remaining on the riverbed.

"If there is black powder that's 150 years old, and if it is dry, then the stability of it has deteriorated," Watts said. "You'd want to be as careful as humanly possible in recovering the stuff."

Once the remains of the Georgia are removed from the river and preserved by experts, the Army Corps will have to decide who gets the spoils. Morgan said ultimately the plan is to put the warship's artifacts on public display. But which museum or agency will get custody of them has yet to be determined.

Right now the Confederate shipwreck legally belongs to the U.S. Navy. More than 150 years after the Civil War began, the CSS Georgia is still officially classified as a captured enemy vessel.