It is both amazing and ironic that the mighty Royal Navy would be forced to combat a warship built in its own shipyard, yet this is what happened at the Battle of Pacocha on May 29, 1877. Built for Peru in 1865, the ironclad Huascar was a model of the monitor type vessel first conceived during the American Civil War. Her displacement was 1300 tons with a length of 67 meters and possessed a very low freeboard. Her sides were protected by 4 ½ inches of armor belt backed by 14 inches of teak. The manually operated gun turret was shielded by 5 ½ inch armor plating and mounted 2x10 inch Armstrong cannon. Huascar furthered carried 2x40 pounder guns on each side and a 12 pounder on the stern. She could speed at 11 knots, carried 300 tons of coal, and a crew of 200.
In contrast, the British had no comparable vessel in South American waters. The forces of the Commander in Chief Pacific Station, Rear Admiral Algernon Frederick Rous de Horsey, included the unarmored frigate HMS Shah and the wooden corvette HMS Amethyst. Shah was a marvelous example of wooden steam ships, built in response to fast American cruisers of the Wampanoag class. She was huge at 6950 tons, swift at 16 knots, and heavily armed with 2x9 inch, 16x7 inch, and 8x64 pounder rifled guns. Amethyst was much lighter at 1970 tons and loaded 14x64 pounders. Shah carried an advanced new precision weapon called the Whitehead torpedo, and the corvette possessed an unguided spar torpedo.
Not surprisingly, Huascar was the pride of Peru's navy when she was seized by revolutionaries in 1877. Captain German Astete was a supporter of a rival politician who sought to overthrow the duly elected President. Astete and his crew proceeded to carry out "acts of piracy" against the Peruvian government. Unfortunately, the pirate ironclad also made the mistake to briefly detain 2 British steamers, whose owners promptly complained to Queen Victoria's representative in Lima. Royal Navy intervention became almost certain after the Huascar defeated a Peruvian naval force consisting of the ironclad Independence, which was twice her size. The decision was made after a British collier was captured.
The two forces met in the Bay of Pacocha on may 29, with de Horsey sending a message to Astete declaring "...I have come to take possession of the (Huascar) in Queen Victoria's name". The Peruvian replied that he would only lower his flag "when there is no longer a single man aboard to uphold it". The bizarre struggle between wood and armor began. The British began the cannonade with their better gunnery at 1700 meters. Sitting low in the water, the Huascar presented a difficult target, and the RN firepower made no dent in the armored hull. De Horsey fruitlessly attempted to improve his firing by closing the range, but the ironclad outmaneuvered him in the shallow bay.
Finally acknowledging the Peruvian battleship's advantage over his gunnery, the Admiral decided to attack with torpedoes. In so doing, the Shah performed the first combat attack by the Whitehead torpedo. The marvel of the age could reach 550 yards at a speed of 18 knots, which proved not enough to catch the nimble Huascar. Again the pirate ironclad escaped harm, to the consternation of the British. Emboldened by the failure of his attackers, Astete increased his fire on the Shah and Amethyst. Choosing reality over pride, Admiral de Horsey ordered his squadron to withdraw. though not without a final attack by the corvette's spar torpedo. When this final attempt ended in failure, the Royal Navy withdrew; a stunning blow to national pride.
The 427 shots fired by the British resulted in only one death on Huascar, while the Royal Navy suffered only a few injured sailors. Two days later, the "pirate ironclad" surrendered to Peruvian authorities, the revolution coming to naught. The mighty rebel warship was later captured by Chile during the War of the Pacific, and exists to this day as a museum ship. De Horsey's action was criticized by Parliament, and ever after the British South American Squadron would consist only of ironclads.