1737-1808. He was born on 25 July 1737 at Cury, near Helston in Cornwall, the son of Edward Kempthorne and his wife, Margaret Tregidgeon.
Kempthorne joined the service from the merchant marine at the age of twenty as an able seaman, and he was commissioned lieutenant on 6 August 1761.
Serving in North American waters upon the Nonsuch 64, Captain Walter Griffith, he joined a force under Captain Samuel Reeve that in May 1778 captured a rebel galley north of the Bristol Ferry on Rhode Island.
Kempthorne was posted captain on 25 September 1781 and joined the London 90 on the Jamaican station. In company with the Torbay 74, Captain John Lewis Gidoin, he fell in with the French Scipion 74 and Sibylle 40 off San Domingo on 17 October 1782, and after a running engagement throughout the afternoon the London was able to open up with a full broadside at 8.30, whereupon the two vessels fell aboard one another inflicting many casualties. Nevertheless the smaller Frenchman was able to work clear and rake the London, and after the two British vessels gave chase the Scipion was lost when she struck a rock and sunk in Samana Bay on the following day. During the action the London suffered eleven men killed and seventy-two wounded. On returning to Jamaica Kempthorne requested a court martial on himself, and was held to have done his utmost to capture the Frenchman.
Kempthorne made his own passage home from Jamaica, and apart from recommissioning the Africa 64 on 3 November 1790 and paying her off on 14 December he remained unemployed thereafter.
He became a rear-admiral on 1 January 1801 and died on 9 June 1808 at his house in Helston, Cornwall.
Kempthorne married Eleanor Sandys of Helston, Cornwall on 4 May 1773 at St. Keverne, Cornwall, and had issue three sons, one of whom predeceased him, and a daughter.