Major Thomas Oswald was appointed Lieutenant-Colonel of the 103rd Regiment of Foot (Volunteer Hunters) on 10 August 1761 and left America. In June 1761, two new regiments had been either raised or formed out of existing independent companies, and thirteen more had been added in August and October. He was congratulated by his late commander General Murray, now Governor of Quebec, in a letter to his brother James Oswald on 9 November 1761. He had been given command of the 103rd, a regiment of the Light Infantry type, formed at Bury St. Edmunds, probably because he had had much experience of light troops with his battalion of the Royal Americans in North America. After the Capture of Belle Île, he was appointed Deputy Governor of the island, as Commandant of the 103rd Regiment of Foot, who had taken part, alongside the Royal Marines, in its capture. The regiment was disbanded in England in 1763 and by 1766 he was included in the list of officers on Half Pay as Lieutenant Colonel.