Sir John Kempthorne (c. 1620 – 19 October 1679) was an officer in the English Royal Navy during the Second and Third Anglo-Dutch Wars, who eventually rose to the rank of Vice-Admiral.

[1] Little is known about the younger Kempthorne's early life, but his father was a Royalist supporter and had served as a cavalry officer in the English Civil War.

The ambassador at Constantinople, Heneage Finch, 3rd Earl of Winchilsea, remarked that 'the captain has always been a man of loyal principles'.

[2] The breakdown of relations between England and the Dutch Republic prior to the Second Anglo-Dutch War led to a period of armament and mobilization.

He escorted several merchant convoys to the Mediterranean between February and May 1667, followed by a period based out of Plymouth to counter Dutch raids.

Kempthorne returned to active service again on the outbreak of the Third Anglo-Dutch War in 1672, with the St Andrew as his flagship.

After seeing the Royal James, the ship of his commander Edward Montagu, 1st Earl of Sandwich, under heavy attack, he made several attempts to come to his relief but was beaten back on each occasion.

[1] Kempthorne was then promoted to rear-admiral of the red, and later vice-admiral of the blue, at which rank he was part of the 1673 campaign under Sir Edward Spragge.

The latter battle led to recriminations and accusations amongst the commanders of the fleet, Kempthorne criticising the conduct of his rear-admiral, Thomas Butler, 6th Earl of Ossory, though he later retracted them.

[1] Kempthorne left the St Andrew in October 1673, drawing a flag officer's pension of £200 per annum.

[1] He became resident commissioner of the navy at Portsmouth, where he became good friends with the governor, George Legge, who had also fought in the Dutch wars.

With the threat of war with France, in 1678 Kempthorne briefly returned to active service, taking up the post of vice-admiral of the narrow seas, with his flag aboard the Royal Charles.