Numbers were again raised in 1803 as hostilities reopened, and, in response to Napoleon's preparations at Boulogne, the Fifteenth were stationed at various points on the Kent coast, including a party at Walmer Castle - much to the pleasure of Lady Hester Stanhope (Pitt's niece).
In 1804 the regiment were reviewed on Wimbeldon Common, by the Duke of York, on the 12th June, and moved into Hampshire. The strength was again augmented - to ten troops of eighty-five - and detachments were sent to escort treasure from four Spanish ships from Plymouth to London.
1805 saw the regiment again increased, this time to 1123 officers and soldiers, and 1062 troop horses. In July the regiment was encamped at Radipole, near Weymouth, as part of a force of eleven thousand of all arms under the Duke of Cumberland, and were repeatedly exercised in front of the King, Queen, and Royal family.
For the remainder of 1805, and throughout 1806, the regiment was stationed at Radipole barracks, and there underwent conversion to Hussars.
Having completed this change, the regiment's Guidons were lodged in St.James', the home of the Duke of Cumberland, in the spring of 1807. The troops were then ordered to be held in readiness for foreign service, but did not leave during that year.
Following a review by the Prince of Wales and the Duke of York on the 20th July on Hounslow heath, the regiment moved to Woodbridge barracks. There, along with the Seventh and Tenth Hussars and two troops of Horse Artillery, they formed the first Hussar Brigade to be seen in England, under the command of Major-General Lord Paget. A review of this Brigade by the Commander-in-Chief on the 5th October drew warm praise.