In accordance with instructions from the Board of War, the new warship cruised in the vicinity of the Newfoundland Banks, on the lookout for British merchantmen.

At 1100, Protector, also flying English colors, hailed the stranger and found her to be the 32-gun letter-of-marque Admiral Duff, bound for London from St. Kitts.

The action ensued for the next hour and one-half, until Admiral Duff caught fire and exploded, leaving 55 survivors for Protector to rescue soon thereafter.

In May 1781, Lloyd's List reported that the rebel frigates Deane and Protector had captured John, Ashburner, master, from Lancaster to St. Kitts, and a ship sailing from Glasgow to Jamaica with 900 barrels of beef and a quantity of dry goods, and had taken them into Martinique.

[7] In June, Lloyd's List reported that the American privateer Protector, of 28 guns and 179 men, had captured Sally, Townsend, master, which had been sailing from St Kitts to New York.

At purchase, the ship was already fitted with a desalination plant which was ideal for the long voyages envisaged to the East Indies and the Danes made contemporary technical drawings of the distilling machine.

When she sailed up the Hooghly to Calcutta the British East India Company suspected that she was American, even though she was flying Danish colours.