By the late 1790’s Britain’s position in Ireland was under threat. Radicals belonging to Wolfe Tone’s United Irishman were actively engaged in military preparations to oppose British rule, and this tempted the French to send troops to their support. In February 1797 a French fleet on the way to Ireland was forced to seek shelter in the Welsh port of Fishguard. The Pembrokeshire Militia captured all the French soldiers put ashore, but the incident did nothing to ease government fears of enemy interference in Irish affairs. One result was a policy of ruthless repression, carried out by locally raised militia and Yeomanry units, that crippled the United Irishmen. In desperation, the remaining radicals rose in revolt, capturing Wexford by the end of May 1798.
In the event, the rebellion was easily put down. Despite a shortage of regular troops and a dismal record of ill disciple among the Irish militia, the British closed in on the rebels, defeating them at Vinegar Hill on 21st June. By then, however, the French had hastily prepared a force of 9,000 veteran troops under General Joseph Humbert, who landed at Killala, County Mayo, on 22nd August. The French, gathering support as they went, advanced to Castlebar and after defeating a British force under Major-General Gerard Lake, crossed the River Shannon. But they could do no more. Lake, reinforced by British regulars, outmanoeuvred Humbert and forced him to surrender at Ballinamuck on 8 September. The threat to British security was over, although the subsequent repression of the Irish people was to be long remembered.
The rebellion was to have an equally long memorial in the British Army. On 12th January 1799 King George III ordered that the 5th (Royal Irish) Regiment of Dragoons, among whom a conspiracy had been discovered during the rebellion, was to be disbanded. It was not re-raised until February 1858, by which time it was regarded as a junior regiment. Thus, when it was amalgamated with the 16th The Queen’s Lancers in 1922, the latter took precedence, producing the seemingly illogical title of 16th/5th.