[3] Méndez Núñez took up his post as a Spanish Navy midshipman on 24 March 1840 and remained at Cádiz until 4 September 1840, then reported aboard the 14-gun brig Nervión at Pasajes on 5 November 1840.

[3] On 7 January 1849 she put to sea from Barcelona to transport Spanish Army troops to Italy as part of an expedition to protect the Papal States[3] during the First Italian War of Independence.

[3] Once the threat to the Papal States had abated, the expedition got back underway on 4 May 1849, participated in the capture of Terracina, then carried out maneuvers as a show of force at Naples, Gaeta, and Porto D'Auro which helped bring the war to an end.

[3] On 18 May Méndez Núñez disembarked at Gaeta and on 29 May Pope Pius IX reviewed members of the Spanish expedition, who displayed for him enemy flags they had captured, and he blessed the Spaniards and gave them thanks by royal order.

[3] Although Cruz was in need of repairs and scheduled for drydocking, Méndez Núñez received orders to carry documents to Havana in the Captaincy General of Cuba, and got underway from Cádiz on 8 February 1852.

[3] Shore duty at the Ministry of the Navy followed, during which he translated into Spanish the 1820 book A Treatise on Naval Gunnery by the British Army officer Howard Douglas.

[3] Under his command, Jorge Juan was off Basilan on 21 August 1860 when she sank five armed boats manned by Moro pirates from Jolo that were headed to the Visayas, took the survivors prisoner, and handed them over to Spanish authorities at Cavite.

[3] Méndez Núñez was promoted to capitán de fragata (frigate captain) on 3 May 1861 and given command of both the schooner Constancia and the Spanish naval division in the southern Philippine Islands.

[3] At dawn on 17 November he launched a second attack, with the landing force supported by gunfire from Arayat and Pampanga, and the Spanish troops reached firmer ground, albeit at a greater distance from the fort, and managed emplace several artillery pieces ashore.

On 29 June 1863, he departed La Guaira to transport the chargé d'affaires of the United Kingdom and Spain and Venezuelan General José Antonio Páez to Puerto Cabello to sign the agreement, which took effect a few days later.

[3] Isabel II arrived at Puerto Plata on the moonless evening of 27 August 1863, where a maritime pilot informed Méndez Núñez that 200 Spaniards were holding out in a fort under siege by 2,000 rebels who planned to attack at dawn.

[3] Leaving Isabel II, he took command of the screw frigate Princesa de Asturias on 22 January 1864[7]and returned to action off Santo Domingo aboard her, establishing a blockade of Manzanillo and Monte Chisti.

[3] Numancia resumed her voyage on the afternoon of 4 February 1865, departing Cádiz with four boilers lit at 16:00 and with provisions for six months, 1,160 tons of coal, gunpowder and projectiles, and a crew of 590 men.

[3] After refilling her coal bunkers, Numancia got back underway on 16 February 1865 to begin a transatlantic voyage,[3][8] initially encountering calm weather in which she made 4 knots (7.4 km/h; 4.6 mph) under sail in light winds after turning off her engine.

[3] On 13 March 1865 she arrived at Montevideo, Uruguay, where she met the brigantine Galiano, the screw corvette Wad-Ras, and the transport steamer Marqués de la Victoria.

[3] They resumed their voyage on the morning of 19 April, and at 10:00 passed Santa Agueda Hill at the southernmost tip of the mainland of South America and end of the Andes.

[3] After they anchored for the night at Fortescue Bay, a warship flying no flag approached, and, given the political tensions in the area, Numancia prepared for action, her crew manning battle stations and loading her guns.

[3] America weighed anchor and departed very early on the morning of 20 April 1865, Numancia following at 07:00 and proceeding in company with Marqués de la Victoria at full speed with eight boilers lit.

News of the defeat prompted Pareja to commit suicide aboard Villa de Madrid off Valparaíso, shooting himself in his cabin on 28 November 1865 while lying on his bed wearing his dress uniform.

At some point during these operations — sources disagree on whether it was on 6 March[11] or on the afternoon of 9 March — Reina Blanca captured the Chilean sidewheel paddle steamer Paquete de Maule, which was bound from Lota, Chile, to Montevideo carrying naval personnel assigned to join the crews of the Peruvian ironclad turret ship Huáscar and broadside ironclad Independencia there;[12] sources disagree on the number of personnel aboard, claiming both a total of 134 men[11][12] and of eight officers and 140 enlisted men.

[8] When Hugh Judson Kilpatrick, the American minister to Chile, learned that Méndez Núñez had been ordered to bombard Valparaíso, he asked the United States Navy commander in the area, Commodore John Rodgers, to attack the Spanish fleet.

[8][18] Several days of negotiations began on 26 April, during which Méndez Núñez granted neutral countries a four-day delay in his attack to give them time to salvage their interests in Callao.

At one point, Numancia struck bottom in 30 feet (9.1 m) of water and had some difficulty pulling off the shoal, overheating her propeller bearings while running her engine in reverse at full power.

[8] but only one shell penetrated Numancia′s armor; the teak wood underneath it absorbed much of the remaining force of the impact, which resulted merely in a few blown-out rivets and a small leak that her crew repaired quickly.

[23][24][25][22] After parting company wih the Philippines-bound ships, the rest of Méndez Núñez's squadron passed around the Cape of Good Hope under sail in winter without warm clothing or fresh food, and scurvy broke out among the crews.

[9] Despite the ceasefire in the southeastern Pacific, Spain did not reach peace settlements with its opponents for years afterward, and so Méndez Núñez, although still recovering from his wounds, remained in command on the South American station with the screw frigates Almansa, Concepción, and Navas de Tolosa, patrolling in the Atlantic Ocean and the Caribbean against possible enemy naval operations and interdicting contraband bound for the southeastern Pacific.

[15] However, government officials were making plans to depose Queen Isabella II and, knowing that his sympathies lay with her and that his great fame after the Chincha Islands War would give him influence on affairs in Spain that would work against their goals, surprised him by denying his request on the grounds that it lacked merit unless he needed to return to Spain because of ill health, and he had made no claim of ill health.

In October 1868, the new Provisional Government′s Minister of the Navy, Juan Bautista Topete, ordered Méndez Núñez back to Spain, informing him that the new government needed the services of someone with his standing and experience.

[26] Further alienated from politics and military men who engaged in them, he focused on reforming the Spanish Navy, instituting "half salaries" for personnel to increase funding for the construction of new ships.

[26] King Alfonso XII visited the chapel on 2 August 1877 and decreed that his remains should be reburied at the Panteón de Marinos Ilustres (Pantheon of Illustrious Sailors) in Cádiz.