The War of Austrian Succession had spread to the Caribbean and French colonies soon became a target also and islands such as Guadeloupe, Martinique and Saint Domingue were under a close blockade by the Royal Navy.

After Knowles finished his stint as governor of Louisbourg he was promoted to rear-admiral of the white on 15 July 1747, and appointed as commander in chief on the Jamaica station.

[3][4] Shortly before midday on 22 March 1748 in HMS Elizabeth Knowles's led his squadron into the harbor of Port Saint Louis, completely surprising its defenders.

An imposing seventy eight gun island castle guarded the road stead, manned by 310 troops and a company of black gunners under Governor Étienne Cochard de Chastenoye behind a twenty four foot-high stone walls.

The French garrison under the terms surrendered, but were soon released and marched away to the safety of the nearest settlement but keeping their firearms and not to fight against any of the British forces for a year and a day.