[3][6] The War of the Austrian Succession having begun in 1740, Aylmer continued to serve in Hector, and he was present in her during the unsuccessful Siege of St. Augustine between April and 5 July of the same year.

[3][8][9] In February 1744 he encountered the East Indiaman Duke of Lorrain being attacked by a Spanish 40-gun privateer and set out to defend the merchant ship; upon Port Mahon's arrival the privateer disengaged from Duke of Lorrain, threw all of her guns overboard to increase her speed and fled from the action.

[8] Continuing to serve around the English Channel, on 10 May Port Mahon captured the French 18-gun treasure ship Le Lion d'Or as the latter attempted to sail from Mississippi to La Rochelle, putting up little resistance before she surrendered to Aylmer.

[3][8] He inherited the title of Baron Aylmer from his father upon the latter's death on 26 June 1754, because his elder brother Matthew had already died in 1748.

[1][10] In 1757 Aylmer was given a pension of £500 per annum by the prime minister, Lord Newcastle, in return for him vacating his position as Comptroller of the Mint in favour of John Buller.