Clouds of silt stirred by the movement of two divers swirled around a beer can sitting upright under 12 feet of water. As the tiny mud particles settled, a startling picture was slowly revealed.

Encircling the can were dark, ruined timbers that once formed gunports of the Jefferson, a U.S. warship that took part in the War of 1812. The Jefferson sank on this spot 168 years ago."It's cold down there," said archaeologist Kevin Crisman as he emerged, shivering, from Lake Ontario. He dumped his scuba equipment and headed for a hot shower - a luxury unknown to the crew of the 20-gun brig as it played cat-and-mouse with the British navy during the summer of 1814.

Crisman's study of the Jefferson, supported partly by the National Geographic Society, is illuminating a nearly forgotten chapter in American history: the struggle between the United States and Britain for control of the Great Lakes. The study also reveals missing links in the evolution of American shipbuilding.

Lessons the designer learned from constructing the Jefferson and similar vessels eventually led to creation of the ship that maritime historians regard as the highest achievement of the age of sail, the peerlessly swift Yankee Clipper.

Crisman pointed to a hand-carved wooden object that resembled a wide canoe paddle, one of more than 1,000 artifacts he has recovered.

"That's a snow shovel," he said. "They had to keep the decks clear during the winter, and this is how they did it."

A variety of the ship's fittings are piled in a nearby warehouse with other relics: British and U.S. coins and military buttons, pieces of fine pottery and plates from the officers' quarters, a cast-iron stove, piles of beef bones, a mustard bottle and the initialed spoon of a sailor who, according to Navy records, deserted in April 1815.

"At least the officers lived well," said Crisman.

The Jefferson was part of a hastily assembled fleet of American ships that opposed the British on Lake Ontario in 1814.

A key element of U.S. war strategy was the conquest of Canada for use in bargaining for concessions from the British. Control of the Great Lakes and Lake Champlain was essential, since these waterways allowed efficient transportation of men, equipment and supplies.

On Lake Ontario, which became the focus of the naval struggle, the United States began the war heavily outnumbered: One 16-gun brig, the Oneida, faced a British squadron of five vessels.

After repelling a British attempt in the summer of 1812 to seize its base at Sackets Harbor, the small American contingent launched a buildup that included buying and arming merchant schooners and constructing more warships.

Capt. Isaac Chauncey, the U.S. commander, hired Henry Eckford, a Scottish shipbuilder in New York City. Working under wilderness conditions at Sackets Harbor, Eckfordand his crew of several hundred shipwrights and laborers quickly turned out seven vessels, including the Jefferson.

The design and exact appearance of the ships has long been a matter of speculation, since no plans or written descriptions have ever been found. Crisman's examination of the Jefferson - the fleet's only surviving wreck - aims to document the nature of the fleet.

Remains of the Jefferson's hull show Eckford had two primary concerns: getting the ships into the water as quickly as possible and making them sail fast.

Built in less than two months in early 1814, the Jefferson had a sharp hull and a shallow draft, forming a fast sailing platform for her 20 guns. Crisman found evidence of construction shortcuts. Unfortunately, the price of her speed was topheaviness. During a storm that September, the captain was forced to jettison half of his cannons to avoid capsizing.

For both sides in the war, the action on Lake Ontario was mostly a matter of nautical feints and parries. Word of a peace treaty came before any conclusive battles could be fought.

Afterward, the Navy virtually abandoned the U.S. fleet. The ships, including the Jefferson, sat at anchor in the harbor for five years until, one by one, they began settling to the bottom. In 1825, they were bought by a local businessman, who proposed to raise some of the hulls for repair and to break up the others for salvage.

For some reason, the hull of the Jefferson was neither raised nor destroyed. Settling into thick mud on its port side, its starboard timbers were soon worn away by ice and waves. The remains then lay undisturbed until the mid-1960s, when a marina was built on the site. Some pilings were driven through gun-ports. Others went straight through the hull, pinning the ship to the bottom.

One day a young couple, unaware of what lay beneath their marina, took their sailboat for a jaunt on the lake. They soon noticed that they were taking on water. On the way out, a protruding timber from the Jefferson had punched a hole through their hull.

"After all these years," says Cris-man, "she's still fighting."