In 1838, in a young republic heady with optimism and national purpose, six ships set sail from Hampton Roads on America's first great global adventure.

They were the vessels of the U.S. Exploring Expedition, a landmark in the annals of science and naval history that in a four-year voyage of extraordinary hazard and industry would discover Antarctica, chart the South Sea Islands, probe volcanoes, make treaties, map the Oregon coast, document Indian languages and advance the frontiers of knowledge in nearly every branch of the physical and life sciences.

They would return laden with 4,000 zoological specimens, including 2,000 new species; 50,000 plants; 2,500 artifacts; and the body of an amiable cannibal king who failed to survive the voyage from Fiji.

But they would also return to bureaucratic bickering, international controversy and a court-martial for their brilliant, stiff-necked and endlessly demanding commander -- and a national ho-hum for their achievements. Though the impact of their discoveries would reach far into the 20th century, their journey itself would largely be forgotten. When expedition leader Charles Wilkes died in 1877, his New York Times obituary made no mention of the voyage.

So vast was the body of knowledge gleaned by the expedition that the Smithsonian Institution had to be built to contain it. Today the Smithsonian's National Museum of Natural History unveils a major new exhibition celebrating the astonishingly little-known undertaking that put American science and naval power on the map.

Packed with everything from pickled vertebrates to pistol-cutlasses, erupting volcanoes and a cinematic trip by square-rigger around Cape Horn, "Magnificent Voyagers: The U.S. Exploring Expedition, 1838-1842" is every bit as rich in wonder as the "Treasure Houses of Britain" exhibition just down the Mall. It will captivate any armchair adventurer who ever dreamed.

The origins of the Wilkes expedition were as wonderful as its results. They appear rooted in the obsession of one John Cleves Symmes Jr., an Ohioan convinced that the world was hollow and that an entrance to the inner world lay at the South Pole. The "holes in the poles" theory was not highly regarded, even then, but New England whaling interests looking for new whaling grounds joined with Symmes and his friends to lobby Congress for an exploratory expedition to the South Seas.

Congress authorized the expedition in 1828, but it was another decade before it sailed, manned by 490 sailors and civilians, including nine civilian "scientifics" who would alter forever the relationship between government and science.

One of them, James Dwight Dana, would become one of America's most distinguished scientific leaders, using his observations of volcanoes during the expedition as the basis for the theory of continental drift.

"The voyage was, in one sense, a scientific declaration of independence," says Dr. Herman Viola, director of the museum's national anthropological archives. American commerce had been almost totally dependent on British charts and science, which rankled in a country that fought off Britain in two successive wars. The nation wanted its own sources for this critical information.

Over a period of four years, the expedition circumnavigated the globe, covering 87,000 miles -- surveying and charting for the first time the coastline of the Pacific Northwest and about 280 islands, including the Hawaiian Islands. The expedition members also prepared important maps of the Oregon Territory and charted about 1,500 miles of the antarctic coast, thereby proving the existence of a continent previously only rumored by seal hunters working the Southern Ocean.

Combining naval and scientific objectives was not always easy. Wilkes, a gifted physicist, artist and surveyor as well as naval officer, later admitted he cultivated the image of a martinet, which he thought helpful to his authority. When the expedition was delayed beyond the two-year enlistment period, a number of sailors sought freedom in Hawaii. When three marines tried to follow, Wilkes had them flogged until they reenlisted. His freedom with the lash, while not unusual in that day, led to a court-martial and public reprimand when he returned.

But Wilkes' drive carried his men to extraordinary efforts. At Rio de Janeiro, when two officers climbed Sugar Loaf Mountain and returned with tales of their exploit, he rebuked them for not taking survey instruments to render the climb "useful." The officers promptly went back to climb again.

In Hawaii he led 200 men to the summit of Mauna Loa volcano for a 42-day study of volcanics and meteorology. The remains of their camp still stand.

The expedition also had a diplomatic and military mission. South Sea natives, particularly in Fiji, had acquired an unfortunate appetite for U.S. seamen, and Wilkes' men were instructed to make the waters safe for American whalers and other ships. They ended up capturing a cannibal chief named Vendovi who cheerfully admitted leading the killing and consumption of several U.S. seamen seven years before. Vendovi was to be taken to America and taught that eating Americans was "the worst thing a Feejee could do." But by the time he finally died two years later upon arrival in New York he had become something of a favorite with the officers and men.

Only two of Wilkes' six ships made it through the voyage. One disappeared with all hands while rounding Cape Horn. Another was wrecked at the mouth of the Columbia River. A third was sent home early and a fourth sold as unseaworthy.

What did make it home was a mountain of artifacts, which took 15 years to process into scientific data. Wilkes himself personally prepared the five-volume "Narrative of the United States Exploring Expedition," plus two scientific volumes on meteorology and hydrography and a two-volume atlas of charts. In all, 23 volumes of scientific data emerged from the expedition, covering everything from botany and herpetology to crustaceans and Pacific geology. Congress finally wearied of funding more.

The artifacts arrived more or less simultaneously in Washington with a $500,000 bequest from a little-known Briton named James Smithson to found in Washington under his name "an establishment for the increase and diffusion of knowledge among men." Housed initially in the Patent Office Building, which now houses the National Portrait Gallery, the "Wilkes collection" ultimately migrated to the Smithsonian, in the process turning the budding institution from a research institute into a museum as well.

Planning for the current exhibition began more than seven years ago with a request to the Smithsonian's Viola for some Pacific artifacts to complement a show at the Bernice P. Bishop Museum in Honolulu. Interest in materials from the Wilkes expedition was so great that Viola eventually developed a slide show on the expedition story, which grew into the concept of a major exhibition celebrating both the voyage and its role in establishing America's national museum.

The exhibition itself, conceived in part to highlight the 75th anniversary of the natural history building, was made possible by a grant from the Atlantic Richfield Foundation. It took almost as long to create as the voyage, and is no less remarkable. Compellingly displayed with such touches as a 55-foot iceberg mural, a re-created lower deck of the flagship Vincennes and personal letters to Dana from Charles Darwin, it should go far toward replacing in the history books the long-neglected saga of Wilkes and his "scientifics."