The Hankey, Yellow Fever, and Nautical Signal Flags
Mosquitoes carry yellow fever.

The Hankey, Yellow Fever, and Nautical Signal Flags

A ship carried yellow fever to America
A ship carried yellow fever to America in 1793. Morguefile photos.

How a Breach of Maritime Custom Changed United States Boundaries

Who would have thought that one ship could have altered American history and redrawn United States boundaries? Or that hoisting a simple yellow signal flag might changed all that?

Water barrels hosted mosquitoes carrying the yellow fever virus.
Wooden water barrels offered the perfect environment for transporting mosquitoes. Morguefile photos.

History professor Billy G. Smith’s new book, Ship of Death (2013), shows how the Hankey, a ship that crisscrossed the Atlantic in 1792-93, played a pivotal role in American history. Or rather, its tiny stowaways did: the ship’s wooden water barrels harbored mosquitoes carrying yellow fever.

As the Hankey visited port after port in the Caribbean and Philadelphia, it left a raging pandemic in its wake. Philadelphia’s epidemic forced George Washington to flee the nation’s first capital. And the decimation of French troops in the Caribbean probably induced Napoleon to give up a huge chunk of land on the American continent: The United States might have the Hankey, and its captain’s failure to hoist the “yellow jack” – the customary warning of disease on board – to thank for the Louisiana Purchase.

An Ill-Fated Voyage Sparks a Yellow Fever Pandemic

Mosquitoes carry yellow fever.
Aedes aegypti mosquitoes can transmit yellow fever. Morguefile photos.

The story started with a group of idealistic British who decided to set up a colony free of slavery on the west coast of Africa. They settled the island of Bolama, cutting down trees for building material and to create farmland. They also brought down several of the trees’ inhabitants: monkeys, a mosquito living in tree canopies and specializing in those monkeys, and a virus inhabiting both. Having lost their habitat, mosquitoes then bit the ground-dwelling humans, infecting them with yellow fever. The virus passed to another species of mosquito, Aedes aegypti, that prefers human blood.

Yellow fever in Buenos Aires
Yellow fever strikes Buenos Aires. “Juan Manuel Blanes Episodio de la Fiebre Amarilla” by Obra de Juan Manuel Blanes (1830-1901) – Museo Nacional de Artes Visuales, Montevideo. Licensed under Public Domain via Wikimedia Commons

Yellow fever decimated the colonists. Some survivors sailed on the Hankey to America on a circuitous route back home, but many of the passengers and crew succumbed to yellow fever en route. Billy Smith found the long-lost log of the Hankey in the British National Archives in Kew, England, and compared the Hankey’s arrival dates at various New World ports with the epidemics that broke out only days afterwards: Barbados, Grenada, Saint Domingue (Haiti), and Philadelphia. The Hankey, writes Smith, “created the first major pandemic of yellow fever in the Western Hemisiphere.” It “killed hundreds of thousands of people around the Atlantic Ocean” and lasted two decades.

Matthew Somerville Morgan, "Yellow Jack Monster" (1873). Library of Congress Prints & Photographs Division, public domain.
Matthew Somerville Morgan, “Yellow Jack Monster” (1873). Library of Congress Prints & Photographs Division, public domain.

In Philadelphia alone, the yellow plague killed 5,000 in 1793. One third of the city’s 50,000 inhabitants fled the city. George Washington took extended leave in Mount Vernon, and Secretary of State Thomas Jefferson stopped going to work. Treasury Secretary Alexander Hamilton remained, but so many other government officials fled that the nation’s nascent government ground to a screeching halt.

Word of the Hankey’s contagion had reached England before it arrived there in late 1793. After disembarking the passengers, the English burnt the Hankey to the waterline and sunk it in the Thames estuary, preventing a major outbreak on the British Isles. Of the original Bolama colonists, only a handful had survived.

Yellow Fever and the Louisiana Purchase

Beyond death and personal suffering, the Hankey’s wake turned political. By far the greatest impact of her voyage was the Louisiana Purchase in 1803. After Napoleon Bonaparte lost thousands of troops in Saint-Domingue, not only to the Haitian Revolution but to yellow fever, he gave up on America and offered Thomas Jefferson the Louisiana Territory. “From Saint-Dominique to Philadelphia, the voyage of the Hankey did more than spread death; it redrew the map of the United States, reconfiguring the political and geographic landscape of the early American republic,” writes Smith.

Yellow fever induced Napoleon to sell the Louisiana Territory in 1803.
United States government, from the Atlas of the United States; public domain.

What if Captain Cox had Hoisted the Yellow Jack?

A captain should have flown the yellow jack if yellow fever was on board.
The “yellow jack” was a square yellow signnal flag indicating disease on board.

It’s fun to engage in some alternate history and ask if any of this would have happened if John Cox, the Hankey’s captain, had complied with maritime custom. He should have flown a yellow flag. The “yellow jack” was the international signal for disease on board. Had Cox hoisted it, the Hankey would have been quarantined and the pandemic possibly prevented.

Philadelphia's waterfront in the 1770s. Balthasar Friedrich Leizelt, "Vuë de Philadelphie," 1770s. Library of Congress Prints & Photographs Division; public domain.
Philadelphia’s waterfront in the 1770s. Balthasar Friedrich Leizelt, “Vuë de Philadelphie,” 1770s. Library of Congress Prints & Photographs Division; public domain.

Did Captain Cox commit a crime? I’ve taken a brief look at that question, but haven’t come up with anything conclusive. King George III did enact a statute in 1806 requiring all ships with infectious diseases on board to fly a signal if they were within four leagues of the British Isles. It’s unclear to what extent that British admiralty law incorporated maritime custom as customary law, and I haven’t found period regulations from the United States mandating a ship to fly the yellow jack.

Whether they were incorporated into statute or not, one this is clear: Nautical signal flags played a critical role in period commerce. One captain’s breach of maritime custom may have changed history beyond his imagination.

Literature on point:

Billy G. Smith, Ship of Death: A Voyage that Changed the Atlantic World (New Haven: Yale University Press 2013)

John Raithby, The Statutes Relating to the Admiralty, Shipping, and Navigation of the United Kingdom (London: Eyre & Strahan 1823)

Written by
Ann Marie
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    • No, he didn’t. He may have developed immunity from previous exposure, because he survived the voyage all the way back to England. But it was the last voyage he ever captained. Then he faded into obscurity. He may have realized, based on news reports from the New World, that he played a role in spreading the yellow fever epidemic.

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