In 1779, when France espoused the cause of America, and sought to harass the mother country in Europe, O'Connell was engaged in the expedition against Portmahon, which is the principal town in Minorca, situated on a rocky promontory, difficult of access from the landward, and defended by Fort San Philipo, in which there was a resolute garrison. O'Connell, with his new regiment, served under the Duc de Crillon at the siege, and conducted himself with such honour as to be specially noticed. The operations were severe and protracted, but in three years the Spaniards and their allies recaptured the whole island of Minorca, which at the peace of 1763 had been formally ceded to Britain. In 1782, O'Connell served with the combined French and Spanish armament which blockaded Gibraltar, during that memorable siege which had commenced on the 12th of January in the preceding year. Having shown considerable skill as an engineer at Minorca, he was one of the council-of-war appointed to assist the Chevalier d'Arcon in conducting the grand attempt in which France and Spain had resolved to try their full strength for the capture of that celebrated rock, the key of the Mediterranean; and for this purpose, as already related in the memoir of the Lacys, 40,000 soldiers, with 200 pieces of cannon and 80 mortars, pressed the attack by land, while 47 sail of the line, 10 battering ships, and a multitude of frigates, mounting 1000 guns and having 12,000 chosen soldiers added to their crews, lay before the fortress by sea--and in that fortress, to meet all this warlike preparation, were only 7000 British soldiers! The French army was commanded by Louis Duc de Crillon-Mahon, the representative of an ancient noble family in the Vaucluse, who had commenced his military career in the Grey musketeers, and served under Marshal Villars in Italy. He had direction of the whole attack; his engineers were the most expert in Europe, and brave volunteers came from all quarters to take part in a siege which attracted the attention and raised the expectation of all Continental Europe. As a member of the council-of-war, O'Connell repeatedly opposed the plans of the Duc de Crillon and of the Chevalier d'Arcon, and declared their system of attack "worthless;" and the sequel, in the triumph of General Elliot, proved that his observations were correct. In the grand attack he accepted command of one of the floating batteries.