[2] Shortly after Almansa entered service, the Chincha Islands War broke out in the southeastern Pacific Ocean between Spain and Chile in September 1865.

[4][3] 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.

[3] The Spanish ships used the delay to prepare for the attack: The frigates all lowered their topmasts and main yards and altered their rigging to reduce the likelihood of damage to their masts, set up on-board field hospitals, and painted over the white stripes on their hulls with black paint to reduce the ships' visibility and give Peruvian gunners less of an aiming point.

Vencedora and the auxiliary ships stood off near San Lorenzo Island while the other six Spanish ships attacked Callao, with Numancia (operating as Méndez Núñez′s flagship), Almansa, and Resolución assigned to bombard the northern part of the harbor while Reina Blanca, Berenguela, and Villa de Madrid shelled the southern part.

At either 14:30[2] or 15:00,[3] according to different sources, a 500-pound (227 kg) Peruvian Blakely shell exploded aboard Almansa and started a fire in the gunpowder storeroom.

[2][3] A disastrous magazine explosion that would have destroyed Almansa appeared imminent and her officers advised Sánchez Barcáiztegui on several occasions to flood the gunpowder storeroom.

[2][3] He did not answer them at first, but on the last occasion they recommended it he explicitly refused, saying: "Today is not the day to wet the gunpowder,"[2][3] a statement that went down in Spanish Navy history.

[4][3] Méndez Núñez's squadron spent the next several days at San Lorenzo Island just off Callao, making repairs and tending to casualties.

[5] Viewing an eastward passage around Cape Horn in winter as too dangerous for his damaged ships, he decided to steam west across the Pacific Ocean.

[2] Almansa and the rest of Méndez Núñez's squadron arrived at the Rio de la Plata (River Plate) on 12 December 1866.

[10] On 24 December 1866, the Ministry of the Navy ordered Méndez Núñez to move to Havana and prepare to defend the Antilles against attack.

[10] Almansa returned to Spain in April 1868 and was under repair during the Glorious Revolution of September 1868, in which Queen Isabella II was deposed.

[2] Almansa operated with Reina Blanca and the screw schooner Ceres on the South American station until 1872, defending Spanish interests during conflicts in the region.

The Cantonal squadron lacked naval officers, and the ships were under the command of a cavalry general, Juan Contreras y Román, wo was aboard Vitoria.

[13] When the city's forces hoisted a black flag in response, the ships resumed fire, this time with 200-pound (91 kg) projectiles.

[17] Facing little opposition from the Cantonalist crews,[18] Swiftsure and Friedrich Carl detained the two ships without prior approval from London or Berlin.

[12][2][14] The Spanish central government incorporated them into its squadron under the command of Contralmirante (Counter Admiral) Miguel Lobo y Malagamba, who made Vitoria his flagship.

[21] Later, during the night of 10–11 October, he ordered his ships to raise sail, probably to economize on their use of coal, and a strong north wind blew his squadron offshore and eastward to a position east of Portmán, Spain.

[21] Vitoria broke off to chase Numancia, leaving Almansa, Carmen, and Navas de Tolosa to face the approaching Tetuán and Méndez Núñez.

[21] Almansa, Carmen, and Navas de Tolosa were steering toward Cartagena in the wake of Numancia and Vitoria,[21] putting them on a converging course with Méndez Núñez.

[20] As the Cantonal Rebellion collapsed, Numancia got underway from Cartagena on 12 January 1874 with 2,000 people aboard and ran the centralist blockade, transporting 1,635 Cantonalist rebels to French Algeria[4][24] pursued by Almansa, Carmen, and Vitoria.

[2] In 1880, Almansa was assigned to the Training Squadron, which was under the command of Contralmirante (Counter Admiral) José Polo de Bernabé.

[2] As part of the squadron, she participated in maneuvers off Galicia on 9 August 1881 presided over by King Alfonso XII and Queen Maria Christina.

[2] On 13 August the king and queen embarked on the armoured frigate Sagunto to head for La Coruña escorted by the rest of the squadron.

[2] The squadron continued to escort the king and queen as they visited the Galician estuaries and was present at the laying of the keel of the unprotected cruiser Reina Cristina at Ferrol, Spain, on 12 August 1881.

[2] Almansa again was assigned to the Training Squadron in Galician waters at the end of August 1884, replacing the screw frigate Lealtad.