Despite an active naval career in which he reached the rank of Rear-Admiral of Great Britain, Knowles found time to continue his studies.

[1] Knowles was assigned to HMS Lyme in June 1721, initially serving as a servant to Captain Lord Vere Beauclerk and, after the first eighteen months as an able seaman.

[3] Having established a reputation as an engineer, after Knowles's return to Britain he was given an advisory and supervisory role in the drawing up of plans for Westminster Bridge.

[7] Having completed the mission and formulated a plan of attack, Knowles was given command of the bomb vessels, fireships and other small boats, and duly bombarded the fortress of San Lorenzo, at the mouth of the Chagres River.

[3][9] Knowles spent the next few months cruising, before returning to England in company with HMS Torrington as an escort for a 25 ship strong fleet of merchantmen.

He soon moved to command the 60-gun HMS Weymouth, and sailed with her from St Helens Roads on 24 October 1740 as part of Sir Chaloner Ogle's fleet to reinforce Vernon in the West Indies.

[3][9] Knowles formed part of Vernon's council of war on 16 February 1741, which resolved to make a naval and land assault on Cartagena.

[3] Knowles took command of the 70-gun HMS Suffolk in 1742, and in 1743 received orders from Ogle to attack the Spanish settlements of La Guaira and Puerto Cabello.

[3][14] The Spanish governor of Venezuela Gabriel de Zuluaga, well informed of the Royal Navy plans, recruited extra defenders and obtained gunpowder from the Dutch.

Between 1743 and 1745 he captured a large number of prizes, with his success leading to a letter addressed to him and signed by 63 of the principal figures in Jamaica; Sir, Though we are certain that the public services you have done, and are continually doing, proceed, as they always will, from the noblest principle, and without the least expectation of popular applause; yet, being fully sensible, and having indeed been immediate partakers of them, we should think it an unpardonable neglect at least, if it did not deserve a worse appellation, should we omit to make our joint acknowledgement thereof, &c.[15] During this period he also found time to design the first British Tower in the west Indies, the 1745 River Fort Barbuda, a very early prototype of the later Martello Tower.

[15][17] He returned to Britain later that year, and in January 1746 he was aboard HMS Canterbury as commander of a squadron in the Downs, under Vice-Admiral William Martin.

[18] He spent nearly two years as governor, and having initially complained to the Duke of Newcastle about the "confused, dirty, beastly condition" of the fortress, was largely engaged in repairing and improving the defences.

On 30 September he fell in with HMS Lenox, under Captain Charles Holmes, who reported that he had encountered a Spanish fleet some days earlier.

[3] In 1754, the Maroons of Crawford's Town rose up in revolt, and Knowles put down the rebellion, defeating and capturing its leader, Quao.

Over his four-year period as governor he took steps to reform the legal system, and also moved the administrative capital from Spanish Town to Kingston, arguing that the latter was more defensible.

[3] On his return from Jamaica, it was proposed to create him a Knight of the Bath, or raise him to an Irish Peerage, but he declined both these honours, though subsequently he accepted a baronetcy.

[26] In 1756 the Cuban governor extended an official invitation to him to pay a visit to Havana, the strongest naval and military Spanish base in the Caribbean and the Americas.

Later he had drawn up plans for the capture of The Havannah which he submitted to William Pitt, probably the same which he laid before the cabinet at the time of his resignation as Prime Minister.

[27] Knowles successfully took the novelist, Tobias Smollett to court for libel, as the editor of The Critical Review, resulting in a fine and imprisonment for three months.

[3][29] Knowles briefly flew his flag aboard HMS Royal Anne in the winter of 1757, but the debacle at Rochefort meant he was soon removed from active service.

[30] Twenty years later a pamphlet lamented “our permitting Sir Charles Knowles to act for that ambitious and formidable state in the capacity of lord high admiral, at a time when his abilities might have turned to great account in his native country."

[35]...a black sea squadron that had achieved permanent paramountcy over the Turks, a reconstructed dry dock, and a new canal for the fraction of the anticipated cost….

[citation needed] Knowles married Mary, the sister of Rebecca, wife of William Bouverie, 1st Earl of Radnor, and Sir John Alleyne, later a Speaker of the Barbados House of Assembly, on 23 December 1740.

[9] The marriage produced a son, Edward Knowles, who followed his father into the navy, but was lost when his vessel, the sloop HMS Peregrine foundered in 1762.

the Court at Petersburg” She was a great favourite of the Empress who made her a maid of honour and presented her with her diamond monogrammed brooch and other jewels.

In writing to Admiral Anson about ship construction, masts, sails, rigging and the treatment of timber in the dockyards he anticipated much of what Kempenfelt was to say nearly forty years later.

Knowles remained intellectually active until the end, writing months before his death to The Reverend Charles William Tonyn “I must beg you will not give yourself any trouble about seeking for a person to copy my manuscript as I wished for one at that time more for your nephew than myself.

Such a One I should be glad to find, & make a companion of.” [46] His family found that he had left no personal papers at his death, although a reason suggests itself in an intriguing letter from Jeremy Bentham to his son “ Blanket a 2d Lieutt on board the Victory …was intimate with Ad Knowles and was over with him one summer in Russia.

He was with him when he died got a great many of his papers and regrets that he did not get more.“[47] John Blankett, later Admiral, shared Knowles' views on ties with Russia having compiled a detailed report for the Admiralty advocating a close alighnment with Russia following a visit to St Petersburgh after the Peace in 1763 [48] His posthumous reputation is suggested in “Plain suggestions of a British seaman” 1794, 4: “We had not in England a man more thoroughly conversant in nautical affairs, or who better considered the interest of our navy”[49] Charlestown, New Hampshire and Charles Town, Jamaica are named after him.