Prowse appears to have been of very humble origins, little is known about his birth or childhood, but he appears to have been born to a working-class Devon family of Cornish origin in 1752. He probably went to sea aboard merchant ships initially, but is first recorded in the Navy on 13 November 1771 as an able seaman aboard the Hamoaze guardship, the 74-gun . Prowse remained aboard her for the next four years, only leaving her on 26 February 1776. His next posting was to the 74-gun , which he joined in November that year, being rated as midshipman and master's mate on 31 August 1778 by Captain George Bowyer. Prowse and the "Albion" were by then serving on the North American station, and went on to see action at the Battle of Grenada on 6 July 1779 and the