One of the last things doomed sailors on board the Union gunboat Tulip heard was a frantic cry from the engine room -- "For God's sake, somebody raise the safety valve!"
As master's mate John Davis rushed toward the commotion, the boiler exploded, blasting him into the Potomac, and sending the Tulip and 46 of its 57 officers and men to the muddy bottom. It was 6:20 p.m. on Nov. 11, 1864.
Beginning Oct. 4, volunteer divers working with Maryland's archaeology office and the U.S. Naval Historical Center will descend to the Tulip's remains, 48 feet under water.
Guided by naval records, the logs of nearby ships and the accounts of survivors like John Davis, they will search for clues to help them reconstruct the disaster. They will scan the bottom for traces of the gunboat's cabin and pilothouse, said to have blown clear of the hull.
Sonar imagery taken in May 1994 and subsequent inspections by divers already appear to confirm that a large section of the starboard hull was ripped away by the blast.
The volunteers will conduct a magnetic survey of the remains, and an assessment of what a more detailed study or excavation or artifacts might reveal.
"The whole point of this is to build a case for what to do next," said Bruce F. Thompson, assistant state underwater archaeologist.
Scientists already have 70 artifacts taken illegally from the wreck by teen-age divers in the 1960s. Tracked down and recovered last year, they are conserved at the Naval Historical Center in Washington.
One goal of this year's mission is to learn more about the "Potomac flotilla" -- two dozen Union gunboats that patrolled the Chesapeake Bay and its tributaries during the Civil War. From Norfolk to the rail bridge at Havre de Grace, they suppressed smugglers and supported federal troops fighting in Virginia.
James S. Schmidt, who studied the flotilla for his 1991 master's ++ thesis at East Carolina University, wrote that its dominance on the water "ultimately crushed Confederate efforts to gain a negotiated peace or foreign intervention and recognition in 1861. The flotilla was crucial to the protection of Union lines throughout the war."
It also proved to be an eager employer of immigrants, free blacks and escaped slaves. Black sailors made up 23 percent of the gunboat crews. Skilled blacks were promoted to every rank and grade short of commissioned officer. But they were paid less than whites -- a policy intended to curb white resentment, which had led to on-board racial tensions.
More crucial to understanding the Tulip disaster, Mr. Schmidt's research also found that the Potomac flotilla was beleaguered by mechanical neglect and failure, repair delays and poorly trained crews.
To get the steam pressure they needed to catch faster blockade runners, "the engineers and firemen often threw grease, tar, pork, or anything that could burn into the furnaces," he wrote.
"Salt and scale accumulated in the boilers," he said. "In the engine, oil holes and channels became clogged. Condensers filled with thick tallow and dirt."
The Tulip, Mr. Schmidt found, had engine problems within months of its commissioning in 1863. Later modifications may have weakened its boilers. Three months before the accident, both boilers were found unfit. Two engineers refused to work with them.
The boat remained in service, but the boat's officers were ordered not to fire the starboard boiler. On the 11th, they were finally told to sail from the flotilla base at St. Inigoes Creek to Washington for repairs.
Acting master William H. Smith, described in The Sun's 1864 account as "a much esteemed young officer," evidently feared that limping upriver with just one boiler would make his 97-foot vessel a sitting duck for rebel shore batteries. Legend suggests he may also have been in a rush to meet his wife, Kate, in Washington.
At 5 p.m., he ordered the second boiler fired up. The blast at 6:20 p.m. was heard back at St. Inigoes, 13 miles away.
Eight unidentified crewmen from the Tulip were buried at St. Inigoes Creek, near a stone monument that since 1937 has marked the nation's smallest military cemetery.
There was no formal Navy investigation. Survivors blamed Smith. Mr. Schmidt says the disaster resulted from "the Navy's rapid expansion, which made inadequate the naval repair facilities and brought on serious shortages in manpower."
The artifacts reclaimed last year were traced after five years of quiet detective work by Virginia sport diver Uwe Lovas, and by Mr. Thompson.
The wreck divers, now in their 40s, told Mr. Thompson they had been looking for snagged fishing lures on what they thought was an old tug. But after a few dives yielded minnie balls -- lead bullets used in the Civil War -- they knew it was an historic wreck. A little research convinced them it was the Tulip.
With four others, they dove on the gunboat for two summers. They declined to speak with The Sun, but Mr. Thompson said their recollections were filled with "a teen-ager's excitement about a romantic adventure."
But all naval wrecks remain Navy property, and what the young adventurers were doing was looting a war grave protected by federal legislation.
"What amazes me is how they kept quiet all these years," Mr. Thompson said. "It was their own consciences that kept them from selling the artifacts."
Over the telephone, and later in face-to-face meetings, the burly, bearded Mr. Thompson gradually won their trust. He persuaded them to give up the items they had rather than face prosecution. "I subtly made it clear that the Navy could call the FBI" to recover the items. "But that's not what we're into," he said.
The men had kept their treasures in remarkable condition, many still wrapped in 1967 newspapers.
Others had been lent to a small museum in Montross, Va.
There is a brass speed log that still registered 7 7/8 knots -- just under the boat's top speed of 8 knots. There also is a bronze porthole, a telescope, decorative brass from an officer's scabbard, tableware and personal items from the officers' quarters.
"This is the largest collection of artifacts from the Potomac flotilla," said Mark J. Wertheimer, 31, the Historical Center's assistant curator.
Alex Elliott, 31, a Navy conservator assigned to Maryland's archaeology office, was astonished. "This will be one of those [exhibits] where people go, 'Wow!' It's a wonderful collection."
The river mud protected delicate inscriptions on brass instruments, and even on a slate used to record engine-room data. A glass goblet and a porcelain sugar bowl emerged without a chip. A brass lantern survived the explosion and a century in the river with its glass globe intact.
Wine and beer bottles, chess pieces, a pipe stem and a silver condiment stand reflect an officer's refinement.
"I don't think life was particularly hard for them, unlike distant duty on the Western rivers, or a long deployment overseas." Mr. Wertheimer said. "Even in a wartime emergency, there were still certain standards for how people are supposed to live and do their jobs."
Anyone with information about the Tulip can call Mr. Thompson at (410) 514-7663.