Salusbury Pryce Humphreys was born at Clungunford Rectory, Shropshire, on 24 November 1778, the third son of Reverend Evan Humphreys and his wife Mary. He entered the navy on 1 July 1790, during the Spanish Armament, serving as a volunteer aboard the 64-gun , which was then under the command of Captain James Vashon. He was next aboard the 50-gun , the flagship of Rear Admiral Sir John Laforey in the Leeward Islands, followed by a posting to the 32-gun , commanded by Captain Matthew Squire. He was rated as able seaman during this last posting, after which he was moved to the 14-gun , commanded by Captain Francis Laforey. His next ship was the 50-gun , under Captain Paul Minchin, where he was rated as midshipman some time before the outbreak of war with Revolutionary France in February 1793. "Severn" conveyed the Governor General of Canada, Lord Dorchester, and his family and suite, to Quebec, returning to Britain in 1794. Humphreys followed Minchin to his next command, the 38-gun , and went out to the West Indies. While serving there, Humphreys was ordered to act as lieutenant of the 14-gun under Captain Henry Evans in April 1796.