Reporting from Newport News, Va. — 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...