Thomas Earle, like virtually everyone else in Liverpool with any money, was interested in privateering, especially during the American War of Independence. The first commissions against the rebel Americans were not issued until April 1777, two years after the first shots were fired at Lexington, as the British government was not sure of the legal position of issuing commissions against rebels and, in any case, was worried that such commissions might be interpreted as recognition of American independence. Meanwhile, American privateers were receiving commissions from Congress and many British (and Liverpool) ships were captured, though quite a few of these were recaptured by ships of the Royal Navy.

Even after April 1777, British shipowners were not all that enthusiastic about making war against the rebels, whose ships tended to be well defended, did not often carry very valuable cargoes and mainly cruised in areas not much frequented by British privateers. All was to change, however, in August 1778 with the authorisation of general reprisals against France. Almost overnight, Britain and especially Liverpool was engaged in a privateering craze greater than ever before. The newspapers were suddenly bursting with news relating to the Liverpool privateers, with advertisements appealing for men, fitting-out news, reports on cruises and successes, information on prize cargoes and, quite soon, flyers for the auction of these prize goods, the High Court of Admiralty being speedy in its hearing of evidence and condemnation of captured ships as ‘good prize’.

On 25 September 1778, just seven weeks after the first commissions against France, the Manchester Mercury published a list of 18 ships with crews from 60 to 150 men which had fitted out or were in the process of fitting out in Liverpool, and it was noted that ‘prizes have been brought in here worth upwards of £100,000.’ Amongst these first comers was the Viper, Captain Philip Cowell, with commissions against both the French and the American rebels and owned by a syndicate of four Liverpool merchants, including Thomas Earle.