Egmont's papers include a long series of related memoranda written by a former South Sea Company factor, Henry Hutchinson, possibly as early as the 1730s, extolling the advantages Britain would gain from a secure presence in the South Pacific.
While the chronology of the documents is unclear, they influenced Anson’s expedition and may have subsequently been updated as fresh information, and new strategic possibilities emerged. It is, however, clear that Hutchinson’s son passed these papers to Egmont in the period between 2 January 1763 and 6 October 1765.
In the official version of the mission, Byron, in the 24-gun frigate HMS Dolphin, one of the first British warships with a copper-sheathed bottom, accompanied by Patrick Mouat in the 20-gun sloop Tamar, was on his way to take over command of the Navy's East Indies Station.
The decision to send the expedition out seems to have been made sometime between the advent of peace in the middle of 1763, and early March 1764, when Byron wrote to the Dolphin's Lieutenant Philip Carteret, telling him to hurry to London or miss the voyage.
Byron's two ships set sail in June 1764, crossed the Atlantic over the southern winter of and made their way slowly down the South American coast to Rio de Janeiro. There, on 22 October Byron revealed his secret orders to a crew who thought they were bound for the Far East.
At the same time, he demonstrated the first signs of a disinclination to follow his instructions.
The orders pointed him towards Pepys Island off the coast of Patagonia, reputedly discovered by Ambrose Cowley in 1683, and suggested that he approach it from the east. While he was directed to the Cape of Good Hope, and instructed to proceed westwards between 33—53°S, he was told that, if circumstance dictated, he could start from Rio and search inside those latitudes from west to east for three hundred leagues.