Notice is hereby given to all such as shall be willing to enlist in the important expedition now on foot for attacking and plundering the most valuable part of the Spanish West Indies to repair to the following gentleman and subscribe their names til a general rendezvous shall be ordered at Philadelphia ...[2]Farmar and his father answered the call and began recruiting a company of men.

Farmar received his captain's commission on January 10, 1741, as he fought alongside the British regulars across the West Indies until the war ended in 1748.

[3] On May 28, 1761, Farmar received a letter from Charles Townshend: I have the satisfaction to inform you that His Majesty has this day been pleased to promote you to the rank of Major in the 34th Regt of Foot commanded by Lord Frederick Cavendish; And I beg leave to add on my own part, that both from my temper and my public situation, I take the sincerist pleasure in every such instance & testimony of His Majesty's approbation conferred upon officers of your distinguished Merit & Rank.He was promoted to serve with the 34th Regiment of Foot under Lord Frederick Cavendish, the younger son of William Cavendish, 3rd Duke of Devonshire.

The surprise attack lasted a little over an hour and failed, costing the Spaniards 500-600 lives compared to the British loss of around 120 men.

An engineer from the 34th Regiment named Archibald Robertson described the aftermath: "Everywhere repulsed and pursued into the very water where numbers of them were killed and drowned!

He declared that all of the inhabitants of West Florida were subjects of England and demanded that they take an oath of allegiance to the British Crown.

Upon returning he found that he had lost his commission and would not be serving as governor of the British West Florida colony.

His wife Mary Anderson Farmar sold most of the family assets and returned to Yorkshire, England.