Sir Charles Wager; in the Kinsale, again with Lord Vere Beauclerk; in the Feversham and in the Lion, till on 30 May 1730 he was promoted to be lieutenant of the Trial. In the following March he was moved to the Lion, flagship of Rear-admiral Charles Stewart [q. v.] in the West Indies.
In 1732 he was promoted to be commander of the Southampton, a 40-gun ship, but apparently for rank only, as he did not take post till 4 Feb. 1736–7, when he was appointed to the Diamond. In her he went out to the West Indies in 1739, and joined Vice-admiral Edward Vernon (1684–1757) [q. v.] at Porto Bello. The place had already been taken, but he was ordered to take charge of the destruction of the forts, which proved to be a work of some difficulty. Still in command of the Diamond, Knowles was sent in the following March to examine the approach to Chagres, and had the immediate command of the bombs and fireships in the attack on the town, 22 March; on its surrender he was appointed governor of the castle pending the destruction of the defences. The work was completed by the 28th, when the squadron withdrew. Towards the end of the year he returned to England and was appointed to the Weymouth of 60 guns, one of the fleet which went out to the West Indies with Sir Chaloner Ogle [q. v.] In the Weymouth, Knowles took part in the expedition against Cartagena in March–April 1741, and acted throughout as the surveyor and engineer of the fleet, examining the approaches to the several points of attack, cutting the boom across the Boca Chica, taking possession of the Castillo Grande, and destroying the captured works before the fleet left.
The pamphlet ‘An Account of the Expedition to Carthagena, with Explanatory Notes and Observations’ (8vo, 1743), which, written in a very bitter tone against the army, was much spoken of at the time and ran through several editions, was generally attributed to Knowles. The preface to the ‘Original Papers relating to the Expedition to Carthagena’ (8vo, 1744), published with Vernon's sanction, describes the author of the pamphlet as ‘an officer of approved abilities and resolution, who did not depend on hearsay and uncertain reports, but was himself an eye-witness of most of the transactions that he has given an account of.’
After the failure at Cartagena, Knowles was moved into the Lichfield, and in the course of 1742 into the Suffolk of 70 guns. In her he commanded a squadron, sent by Sir Chaloner Ogle in the beginning of 1743 to act against the Spanish settlements on the Caracas coast. No pains were taken to keep the expedition a secret; the Spaniards had two months' warning for their preparations; and the Dutch, though allies of the English, supplied them with powder. The result was that when the squadron attacked La Guayra on 18 Feb. 1742–3 it was beaten off with very heavy loss, and when, having refitted at Curaçoa, it attacked Porto Cabello on 15 April and again on the 24th, it had no better success. On 28 April a council of war decided that ‘the squadron was no longer in a condition to attempt any enterprise against the enemy,’ and Knowles, sending the ships and troops to their respective stations, returned to Jamaica.
He was then appointed an ‘established’ commodore, or as it is now called a first-class commodore, with his broad pennant in the Superbe and afterwards in the Severn, and continued during 1743–4–5 as second in command on the Jamaica and West Indian station under Ogle. Towards the end of 1745 he returned to England, and after a short time in the Downs, as second in command under Vice-admiral William Martin [q. v.], he was, early in 1746, sent out as governor of Louisbourg, which had been captured from the French a few months before [see Warren, Sir Peter]. There he remained for upwards of two years, repairing and renewing the defences of the fortress. In the large promotion of 15 July 1747 he was made rear-admiral of the white, and at the same time was appointed commander-in-chief at Jamaica.
In February 1747–8, with his flag on board the Cornwall, he took the squadron along the south coast of Cuba, and after capturing Port Louis on 8 March arrived off Santiago on 5 April. An attack was immediately attempted, but Captain Dent in the Plymouth, who led in, found the passage blocked by a boom, which he judged too strong to be forced. He turned back, and the ships following did the same. A second attempt was considered unadvisable. Knowles was much annoyed by the failure. Dent, who as senior officer had been for a short time commander-in-chief before Knowles's arrival, was not, perhaps, inclined to undertake any extraordinary service, the credit of which, if successful, would be placed to the account of the newly arrived admiral. Knowles doubtless believed this to be the case, and sent Dent home to be tried on a charge of not having done his utmost. Nearly a year later the court-martial took place and relieved Dent of all blame.
Meanwhile Knowles, having refitted the ships at Jamaica, took them for a cruise off Havana in hopes of intercepting the Spanish
