[3] Beatty was appointed second surgeon's mate aboard the 64-gun third-rate ship Dictator, but was soon reassigned, moving to the 32-gun frigate Iphigenia in September 1791.

He was promoted to first surgeon's mate of the 32-gun frigate Hermione on 1 February 1793, the same day that Revolutionary France declared war on Britain.

[5] On 25 June 1794, he was appointed acting surgeon of the 28-gun frigate Alligator at Port-au-Prince, where he was immediately confronted with an epidemic of yellow fever in which 50 men, one-quarter of the crew, died.

The British were delighted to discover that the ships were loaded with gold bullion and other valuable cargoes, realizing prize money totalling £652,000.

[9] Beatty left the Alcmene in March 1801, to serve aboard the 36-gun frigate Resistance until January 1802, when the Peace of Amiens was signed, and the war between France and England came an end.

In July, Beatty was warranted surgeon of the 74-gun ship of the line Spencer, which was deployed in the blockade of Brest throughout the stormy winter months, and into the next year.

Beatty relates how gases from the corpse caused the barrel lid to open on 28 October 1805, alarming the posted marine guard.

[16] As Victory approached the Nore, Beatty performed an autopsy, removing the fatal musket ball (now in the Royal Collection at Windsor Castle[17]) and later writing a report A Concise History of the Wound.

[18] Victory was decommissioned in January 1806, and Beatty was posted as surgeon-in-charge of Sussex, the former HMS Union and now a hospital ship at Sheerness.

[19] Beatty was appointed physician of the Channel Fleet on 25 September 1806, having received the necessary medical degree from the University of Aberdeen on 28 February 1806.

His duties were shore-based and mostly administrative, though in 1807, number of other naval surgeons and he were active in promoting the new practice of vaccination against smallpox.

He settled at 43 York Street, Paddington, London, and served as a member of the organising committee for the building of Nelson's Column in Trafalgar Square.