The world will soon get its first good look at the wreckage of the only U.S. Navy ship sunk in combat in the Gulf of Mexico during the Civil War, thanks to sophisticated 3-D sonar images that divers have been collecting this week in the Gulf's murky depths.

The USS Hatteras, an iron-hulled 210-foot ship that sank about 20 miles off the coast of Galveston, Texas, in January 1863, has sat mostly undisturbed and unnoticed since its wreckage was found in the early 1970s. But recent storm-caused shifts in the seabed where the Hatteras rests 57 feet below the surface have exposed more of it to inspection, and researchers are rushing to get as complete an image of the ship as possible before the sand and silt shifts back....