Sir John Henslow (9 October 1730 – 22 September 1815) was a Surveyor to the Navy in the British (Royal Navy), a post he held jointly or solely from 1784 to 1806.

He was 7th child of John Henslow, a master carpenter in the dockyard at Woolwich.^[1]

• 1745 Apprenticed to Sir Thomas Slade
• 1762 Master Boat Builder at Woolwich
• 1771 Assistant Surveyor to the Navy
• 1784 Surveyor to the Navy
• 1793 Knighted
• 1806 retired to Sittingbourne, Kent

Cape Henslow on Guadalcanal is named after him.

From 1793 he worked jointly with William Rule.^[2]

Among the vessels he designed were the Acute-class gun-brigs and four frigates to the same design, the first of which was Phoebe. He also designed the Bloodhound-class gun-brigs and Conquest-class gun-brigs. The Laurel-class post ship sixth rates were a series of six ships built to his 1805 design. Perhaps his smallest vessels were the two Placentia-class sloops of 42 tons burthen, which he designed for coastal patrol duties off Newfoundland.

His son John Prentis Henslow, solicitor, was father of John Stevens Henslow. He was also the grandfather of Francis Hartwell Henslowe, who was the son of Edward Prentis Henslow.