[1] However Horace Walpole wrote, ”There was a young Scot, by name Clarke, ill-favoured in his person, with a cast in his eyes, of intellects not very sound, but quick, bold, adventurous.”[2] Clerk entered the Army as a second lieutenant in Cotterrell's Marines with seniority 11 June 1741.
In 1747 Clerk was an engineer with the Anglo-Dutch troops defending the town of Bergen-op-Zoom against the besieging French army led by Count Löwendahl.
After a long and destructive siege the town was taken by a surprise assault and Clerk captured; “being pursued into a house where the enemies fired at him through a door, he opened it and told them he was related to Marshal Löwendahl, who would reward them for saving him.
In Clerk's own words, “In returning from Gibraltar in (April) 1754, I went along Part of the western Coast of France to see the Conditions of some of their Fortifications of their Places of Importance, on purpose to Judge if an Attempt could be made with a Probability of Success....
Command of the expedition was given to Lt-Gen Sir John Mordaunt and "Clerk was appointed Chief Engineer, and the unprecedented step was taken of promoting him at a bound to the rank of Lieutenant-Colonel, he being at the time only a Lieutenant (Commission Book, No.
Under him were Sub-Engineers Richard Dudgeon and Thomas Walker, and Practitioners Robert G. Bruce, Augustus Durnford, William Roy, and John C.
Despite this, Clerk was further employed the next day in accompanying Maj-Gen Conway and Col Wolfe to carry out further reconnaissance of the proposed landing sites at Châtelaillon.
Without their evidence we should have landed, and must have marched to Rochefort; and it is my opinion that the place would have surrendered or been taken in forty-eight hours.”[7] Clerk was quizzed at some length and, though being always careful to say he could only say what he had seen more than 3 years before, he maintained his assertion that not all of the ditch around the town could be flooded as parts of it were higher than the tide could reach.
These, with myself, make five very odd characters, and for the oddity of the mixture I mention it to you.”[1] Clerk's particular talents were much lauded by some; Lord Bute said of him, “With regard to Clarke, I know him well: he must be joined to a general in whom he has confidence, or not thought of.
Never was a man so cut out for bold and hardy enterprises; but the person who commands him must think in the same way of him, or the affair of Rochfort will return.”[8] This was a prescient remark because even as it was written on 8 September 1758, Clerk's impetuosity was getting him into trouble.
Clerk's conduct in this action led to his arrest: “General Blighe… had been actuated, during the course of these enterprises, by a young Lord Fitz-morrice and the adventurer Clarke, who diverted himself from the ships with the difficulties his comrades found in re-embarking.