"The Heart of the USS Monitor"

When archaeologists and Navy divers recovered the warship Monitor's steam engine from the Atlantic in 2001, the pioneering Civil War propulsion unit was enshrouded in a thick layer of marine concretion.

Sand, mud and corrosion combined with minerals in the deep waters off Cape Hatteras, N.C., to cloak every feature of Swedish American inventor John Ericsson's ingenious machine, and they continued to envelop the 30-ton artifact after nine years of desalination treatment.

This month, however, conservators at the Mariners' Museum here and its USS Monitor Center drained the 35,000-gallon solution in which the massive engine was submerged and began removing the 2- to 3-inch-thick layer of concretion with hammers, chisels and other hand tools.

Working slowly and carefully to avoid harming the engine's original surface, they stripped off more than two tons of encrustation in their first week of work, gradually revealing the details of a naval milestone that had not been seen since the historic Union ironclad sank in a storm in December 1862.

"This is a technological marvel. It was cutting-edge in its day. But what's really neat is revealing all the wheels, oil cups, valves and other parts that the Monitor's crew used to operate the engine," said conservation project manager Dave Krop.

"If you consider that it spent nearly 139 years underwater, it's in outstanding shape — though some of the wrought iron has seen better days. And there are some copper alloy parts that look brand-new when they're first uncovered — like they just came off the shelf."

Smaller, more compact, yet just as capable as other steam engines of its day, the Monitor's vibrating side-lever engine was the ideal match for Ericsson's revolutionary warship.

Its long, low, horizontal cylinder enabled the engineer to place it below the vessel's waterline as well as behind a thick armor belt — and that well-protected position virtually eliminated the vulnerability associated with the much larger and more easily targeted engines of the day, most of which towered above the deck of a ship.

Ericsson was so confident in his engine's capabilities that he ignored orders to equip the vessel with masts and rigging.

And it astounded Union and Confederate observers with the way it performed in its historic clash with the rebel warship Virginia — also known as the Merrimac — in the March 8, 1862, Battle of Hampton Roads.

"If the turret and the guns were the Monitor's muscle, this steam engine was its heart," said historian Jeff Johnston of the Monitor National Marine Sanctuary.