John Clerk

John Clerk of Eldin FRSE FSAScot (1728–1812) was a Scottish merchant, naval author, artist, geologist and landowner. The 7th son of Sir John Clerk of Penicuik, Bt, Clerk of Eldin was a figure in the Scottish Enlightenment, best remembered for his influential writings on naval tactics in the Age of Sail.

From an early age, Clerk had been interested in shipping, and had cultivated contacts among owners, sailors, and others involved in seafaring. He made the acquaintance of engineer and sometime naval architect Patrick Miller of Dalswinton, who encouraged Clerk's interest in nautical matters. In about 1770, a former Royal Navy officer, Commissioner Edgar, took up retirement in the village of Eldin where Clerk lived. Inevitably he met Clerk, and shared stories of his experiences at sea. Edgar appears to have taken a keen interest in naval tactics, and was the key source for Clerk of Eldin's writings. As well as relying on Edgar's personal experience and knowledge, Clerk began to research naval tactics through the memoirs of former officers and campaigns.

The British defeat at the Battle of the Chesapeake may have been the event that led to Clerk moving on from studying tactics, to theorizing and writing about them. In doing so, he broke new ground in English naval tactics. While technical manuals, notably signaling books and the various Fighting Instructions, had been published before, no study of naval tactics had been written in English. In his Essay on Naval Tactics, Clerk expounded on the tactic known as "cutting the line". This involved sailing into the enemy's line of ships, and attacking the rear ships of the enemy's line with the whole force of the attacking fleet. Horatio Nelson used several sentences from Clerk's work in his orders to the British fleet before the Battle of Trafalgar.