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. He had served under Admiral
John Byng, and was a friend of Admiral
Edward Boscawen. 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, such as the
Mediterranean operations during the
War of the Austrian Succession by Admiral
Thomas Mathews in 1744, and also more recent events, such as the
Battle of Ushant, which led to a court case between Admirals
Augustus Keppel and
Hugh Palliser. The unexpected British defeat at the
Battle of the Chesapeake may have been the event that led to Clerk moving on from studying tactics, to theorising and writing about them. In doing so, he broke new ground in English naval tactics. While technical manuals, notably signalling books and the various
Fighting Instructions, had been published before, no study of naval tactics had been written in English. The earlier 1762 work of Christopher O'Bryen, which is sometimes advanced as such, was merely an abridgement and translation of the late 17th century works of the French writer Father
Paul Hoste, and of the same genre as the
Fighting Instructions. In his
Essay on Naval Tactics (1779, published 1790), 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. ==Etchings==