On this year's Juneteenth, the oldest known celebration commemorating the abolition of slavery in the United States, consider one of the nation's first cases involving the violation of its incipient slave-trade laws: the "Ganges Incident."

The USS Ganges, originally built for trade in the West Indies, was purchased in 1798 by the federal government to deter French privateers from ransacking U.S. shipping. It left Philadelphia's port that year, the first warship to sail under the American flag since the Continental Navy's last ship, the Alliance, was decommissioned in 1785.

Escorting American vessels en route to Havana in the summer of 1800, the Ganges spotted two U.S. merchant ships, the Prudent and the Phoebe, off the coast of Cuba. Between the two of them, more than 100 individuals from Guinea were found chained below deck.

While Northern states had gradually abolished slavery, it was still legal in 1800. However, to prevent New England ships from participating in the trans-Atlantic slave trade, Congress passed the 1794 Federal Slave Trade Act, prohibiting American ships from transporting slaves.

Sailors in a similar position to the crew of the Ganges often took possession of the human cargo and sold them as "salvage" in Southern ports, such as Charleston and Savannah.

Not John Mullowny, the Ganges' captain. He ordered both ships to sail for Philadelphia, a city with an established reputation for abolitionist sympathies.

"Arrived at the Lazaretto yesterday, 118 Black People, without the least clothing, being taken on board the schooner Phebe, prize to the United States ship Ganges," ran a call placed in the Pennsylvania Gazette, referring to the quarantine station in Essington, on the west bank of the Delaware River. "The humane citizens are requested to send to the Health-Office, at the State House, any kind of linen clothes for their accommodation, as well as to prevent the shock their decency will be exposed to by so many of both sexes being thus exposed naked."

A sympathetic federal judge ruled in favor of the illegally captured Guineans - with each given the legal surname of Ganges - and placed them in the care of the Pennsylvania Abolition Society to work as indentured servants.

Neither enslaved nor fully free, they worked with mostly Quaker shopkeepers and farmers for various lengths of time. Unlike many other indentured servants during this period, the terms of the Ganges' indentures specified the provision of an education. These records are held at the Historical Society of Pennsylvania, allowing descendants of those rescued by the Ganges to trace their family histories.

"This is a story that could really only have happened in Philadelphia," said V. Chapman-Smith, a special assistant at the National Archives. "You had a city with strong antislavery sentiment, a sympathetic federal judge, and a U.S. Navy warship in a position to go out and do something about it."