Writing to the Earl of Camden, the Secretary of State for War, in 1804 about the Camden's nephew who had abandoned a naval career due to seasickness, Nelson acknowledged his own struggles with the condition ever since joining the navy at the age of 12.

"I am ill every time it blows hard and nothing but my enthusiastic love for my profession keeps me one hour at sea," he wrote from his flagship HMS Victory.

This was not the first time Nelson made mention of his debilitating problem.

Seasickness put him "confoundedly out of humour" he wrote in 1776 after a post-malarial bout of vomiting, while in 1793, in command of HMS Agamemnon, Nelson and his stepson were both recorded as seasick in a strong gale off the southern English coast.

By 1804, Nelson had risen to commander-in-chief of the British fleet in the Mediterranean, then the largest naval force in existence.

The nation's pre-eminent sailor however, even after 30 years of service, had not beaten the problem.

But there is more to Nelson's expression of suffering than meets the eye, naval historians say.

"Nelson used his seasickness as a means of expressing his patriotism, duty and sacrifice," said James Davey, Curator of Naval History at the National Maritime Museum.

"The implication is that while the Earl of Camden's seasick nephew might not have stuck at it, Nelson will suffer on for his country."

He told Reuters: "It's very revealing of his character. Patriotic, but not reticent about showing it."

In October 1805, almost a year to the day after he last communicated with Camden, Nelson was killed by a sniper at the Battle of Trafalgar.

On the brink of victory over the combined French and Spanish fleets, he died in the arms of his senior officers.

What became of the Camden nephew is uncertain. After apparently contributing to the loss of a store ship during his brief service, the navy is unlikely to have missed him, but the letter remained in the private archives of the Camden family until recent re-discovery.

It is now on display at the Tunbridge Wells Museum in Kent, 40 miles southeast of London, and can be seen as part of exhibition on the possessions of local noble families. (Reporting by Peter Schwartzstein, editing by Paul Casciato)

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