Sir John Kempthorne was born around 1620, the second son of John Kempthorne, attorney, of Ugborough, Devon, and royalist cavalry officer in the civil wars. His mother was Agnes Simon and he married Joanna (d. 1691), a servant to Lady Bendish, the wife of the ambassador to Constantinople around 1649. John began his naval life as apprentice to the master of a Topsham vessel and rose to command Levant Company ships in the Mediterranean trade.
In "Portsmouth Parish Church", Lilley and Everitt tell of the time in 1657 when, Kempthorne, then master of the Eastland Merchant came across the Spanish pirate known as Papachino. A furious fight followed and Kempthorne found he was running short of round shot. He resorted to firing pieces of eight which ripped Papachino's sail to shreds. This did not prevent the Spaniard prevailing, but such was his admiration for Kempthorne that he treated him well and released him as soon as possible. Kempthorne was able to repay the favour the following year, when Papachino was himself captured and imprisoned in the Tower, by arranging his release by exchange.
In 1664 Kempthorne, a royalist by sympathy, obtained his first naval command during the Second Anglo-Dutch War. He was captain of the Kent and then the Dunkirk before on 26 November he transferred to the first-rate Royal James, which he commanded in the battle of Lowestoft on 3 June 1665 as flag captain to Prince Rupert of the Rhine. On 19 July he transferred to the Old James, whose captain, the Earl of Marlborough had been killed in the action. Kempthorne moved from her to the Royal Charles in February 1666, commanding her as flag captain to the Duke of Albemarle (George Monck) in the Four Days' Fight of 1-4 June before moving to the Defiance on 10 June, becoming rear-admiral of the Blue squadron in her in September. His ships convoyed the Mediterranean trade between February and May 1667 when the squadron sailed for Ireland, remaining there until the end of September. After leaving the Defiance in December 1667, he commanded the Warspite. Despite serving in His Majesty's Navy Kempthorne was also a leading ship owner in the Mediterranean trade.
Kempthorne took command of the Mary Rose in 1669 escorting Lord Howard to Morocco as ambassador. After landing him at Tangier, Kempthorne and a convoy of merchantmen were attacked north of Cadiz on 18 December by seven Algerine corsairs. The fighting lasted that day and much of the next, with six of the Algerine force attacking Kempthorne's single warship. Despite severe damage to her masts and rigging, the Mary Rose managed to disable the enemy admiral's vessel, at which point the whole Algerine force withdrew. Kempthorne's squadron arrived safely in Cadiz Bay on the 20th. The action earned a knighthood for Kempthorne. In the Third Anglo-Dutch War he became rear-admiral of the blue once more, flying his flag in the St Andrew and fighting at the battle of Solebay on 28 May 1672. Kempthorne subsequently became rear-admiral of the red, and remained in the St Andrew for the 1673 campaign, where he was wounded at the battle of Texel, serving under Sir Edward Spragge as vice-admiral of the blue.
From October 1673 Kempthorne drew a flag officer's pension of £200 per annum, and served both as master of Trinity House in 1674-5 and as the first steward of the club for naval captains set up in 1674. On 25th November 1675 he was appointed Commissioner of the Navy at Portsmouth, succeeding Sir Anthony Deane and forming a close relationship with the governor, Colonel George Legge, later Lord Dartmouth, a fellow naval veteran of the Dutch wars. During the naval mobilization which occurred in 1678, Kempthorne held his last seagoing command, in the post of vice-admiral of the narrow seas and flying his flag in the Royal Charles.
In 1676 Kempthorne became a Burgess of Portsmouth and in February 1679, through Legge's good offices, he was returned as one of the MPs for Portsmouth, alongside Legge, in the elections for a new parliament but his parliamentary career was short-lived as he died at Portsmouth on 19 October 1679. He had three sons, to whom he bequeathed shares in five ships. All three became captains in the Royal Navy and died in the service of their country.
He was buried in St Thomas's Church where a memorial was erected to him. In his "History of Portsmouth" dated 1817, Lake Allen says that Kempthorne's body was interred to the left of the altar, where the memorial would have been originally sited. It is now positioned on the Eastern wall of the Navy Aisle.
Dictionary of National Biography, article by J. D. Davies
"Portsmouth Parish Church" by H.T. Lilley and A.T. Everitt
"History of Portsmouth" by Lake Allen
Memorials in Portsmouth
History of Parliament Online