Monitor (warship)

HMS Marshal Ney. The large gun turret is typical of a monitor type warship.

A monitor was a relatively small warship which was neither fast nor strongly armoured but carried disproportionately large guns. They were used by some navies from the 1860s, during the First World War and with limited use in the Second World War. During the Vietnam War they were used by the United States Navy.[1] The Brazilian Navy's Parnaíba is the last monitor in service.

The original monitor was designed by John Ericsson in 1861 who named it USS Monitor. They were designed for shallow waters and served as coastal ships. The term "monitor" also encompassed more flexible breastwork monitors, and was sometimes used as a generic term for any turreted ship.

The term "monitor" also encompasses the strongest of riverine warcraft, known as river monitors. In the early 20th century, the term "monitor" was revived for shallow-draft armoured shore bombardment vessels, particularly those of the Royal Navy: the Lord Clive-class monitors carried guns firing heavier shells than any other warship ever has, seeing action (albeit briefly) against German targets during World War I. The Lord Clive vessels were scrapped in the 1920s.

Officers of a Union monitor, probably USS Patapsco, photographed during the American Civil War
USS Monitor, the first monitor (1861)

Nineteenth century

U.S.Navy monitors forcing the surrender of the casemate ironclad CSS Tennessee during the Battle of Mobile Bay

American Civil War

In Latin, a monitor is someone who admonishes—that is, reminds others of their duties—which is how USS Monitor was given its name.[citation needed] She was designed by John Ericsson for emergency service in the Federal navy during the American Civil War (1861–65) to blockade the Confederate States from supply at sea. Ericsson designed her to operate in shallow water and to present as small a target as possible, the water around her acting as protection.

Nathaniel Hawthorne described Monitor thus:

At no great distance from the Minnesota lay the strangest-looking craft I ever saw. It was a platform of iron, so nearly on a level with the water that the swash of the waves broke over it, under the impulse of a very moderate breeze; and on this platform was raised a circular structure, likewise of iron, and rather broad and capacious, but of no great height. It could not be called a vessel at all; it was a machine—and I have seen one of somewhat similar appearance employed in cleaning out the docks; or, for lack of a better similitude, it looked like a gigantic rat-trap. It was ugly, questionable, suspicious, evidently mischievous—nay, I will allow myself to call it devilish; for this was the new war-fiend, destined, along with others of the same breed, to annihilate whole navies and batter down old supremacies. The wooden walls of Old England cease to exist, and a whole history of naval renown reaches its period, now that the Monitor comes smoking into view; while the billows dash over what seems her deck, and storms bury even her turret in green water, as she burrows and snorts along, oftener under the surface than above. The singularity of the object has betrayed me into a more ambitious vein of description than I often indulge; and, after all, I might as well have contented myself with simply saying that she looked very queer.

Going on board, we were surprised at the extent and convenience of her interior accommodations. There is a spacious ward-room, nine or ten feet in height, besides a private cabin for the commander, and sleeping accommodations on an ample scale; the whole well lighted and ventilated, though beneath the surface of the water. Forward, or aft (for it is impossible to tell stem from stern), the crew are relatively quite as well provided for as the officers. It was like finding a palace, with all its conveniences, under the sea. The inaccessibility, the apparent impregnability, of this submerged iron fortress are most satisfactory; the officers and crew get down through a little hole in the deck, hermetically seal themselves, and go below; and until they see fit to reappear, there would seem to be no power given to man whereby they can be brought to light. A storm of cannon-shot damages them no more than a handful of dried peas. We saw the shot-marks made by the great artillery of the Merrimack on the outer casing of the iron tower; they were about the breadth and depth of shallow saucers, almost imperceptible dents, with no corresponding bulge on the interior surface. In fact, the thing looked altogether too safe; though it may not prove quite an agreeable predicament to be thus boxed up in impenetrable iron, with the possibility, one would imagine, of being sent to the bottom of the sea, and, even there, not drowned, but stifled. Nothing, however, can exceed the confidence of the officers in this new craft. It was pleasant to see their benign exultation in her powers of mischief, and the delight with which they exhibited the circumvolutory movement of the tower, the quick thrusting forth of the immense guns to deliver their ponderous missiles, and then the immediate recoil, and the security behind the closed port-holes. Yet even this will not long be the last and most terrible improvement in the science of war. Already we hear of vessels the armament of which is to act entirely beneath the surface of the water; so that, with no other external symptoms than a great bubbling and foaming, and gush of smoke, and belch of smothered thunder out of the yeasty waves, there shall be a deadly fight going on below—and, by and by, a sucking whirlpool, as one of the ships goes down.[2]

The Battle of Hampton Roads (March 1862), between Monitor and CSS Virginia, was the first engagement between ironclad vessels. Several such battles took place during the course of the American Civil War, and the dozens of monitors built for the United States Navy reflected a ship-to-ship combat role in their designs. However, fortification bombardment was another critical role that the early monitors played, though one that these early designs were much less capable in performing.

Three months after the Battle of Hampton Roads, John Ericsson took his design to his native Sweden, and in 1865 the first Swedish monitor was built at Motala Warf in Norrköping, taking the engineer's name. She was followed by 14 more monitors. One of them, Kanonbåten Sölve, served until 1922 and is today preserved at the Maritiman marine museum in Gothenburg.

Ericsson and others experimented greatly during the years of the American Civil War. Vessels constructed included a triple-turreted monitor, a class of paddlewheel-propelled monitors, a class of semi-submersible monitors, and a class of monitors armed with spar torpedoes.[citation needed]

1866 to 1878

In the 1860s and 1870s several nations built monitors that were used for coastal defense and took the name monitor as a type of ship. Those that were directly modelled on Monitor were low-freeboard, mastless, steam-powered vessels with one or two rotating, armoured turrets. The low freeboard meant that these ships were unsuitable for ocean-going duties and were always at risk of swamping, flooding and possible loss. However, it greatly reduced the cost and weight of the armour required for protection, and in heavy weather the sea could wash over the deck rather than heeling the ship over.

Attempts were made to fit monitors with sails, but the provision of masts interfered with the turrets' ability to operate in a 360-degree arc of fire and the weight of masts and sails aloft made the ships less stable. One ship, HMS Captain, which combined turret and sails with a low freeboard, was lost in heavy weather.

War of the Pacific

Huáscar anchored in the harbour at Talcahuano

A late example of a vessel modeled on Monitor was BAP Huáscar, designed by Captain Cowper P. Coles, the advocate and developer of turret ships for the Royal Navy. Huáscar was one of many monitor designs to be equipped with a ram. She was built and launched in 1865 for the Peruvian Navy at Birkenhead, England, and attained fame in the Battle of Pacocha during the Peruvian Civil War of 1877.

BAP Huáscar, under the command of Rear Admiral Miguel Grau, fought with distinction during the War of the Pacific. Huáscar successfully raided enemy sea lanes for several months and delayed an invasion of the Chilean Army into Peruvian territory until she was captured by the Chilean Navy at the Battle of Angamos in 1879. Once in Chilean hands, Huáscar fought a small battle with the Peruvian monitor Manco Capac, during the bombardment of Arica, where she was damaged; after the land battle was lost, the crew scuttled BAP Manco Capac to prevent capture.

Over the years, both Chile and Peru came to venerate the ship and the officers from both sides that died on her deck, either commanding her or boarding her, as national heroes. Huáscar is currently commissioned in the Chilean Navy, has been restored to a near-original condition and, as a museum ship, is open to visitors at its berth in Talcahuano.

USS Monterey, a breastwork monitor, at Mare Island Naval Shipyard, c.1896. The older Ericsson-designed monitor USS Camanche is visible in the background.


In an effort to produce a more seaworthy vessel that was more capable in ship-to-shore combat, a type called the breastwork monitor became more common in the later nineteenth century. These ships had raised turrets and a heavier superstructure on a platform above the hull. They were still not particularly successful as seagoing ships, because of their short sailing range and the poor reliability of their steam engines. The first of these ships was HMVS Cerberus, built between 1868 and 1870. She was later sunk and used as a breakwater near Melbourne, Australia and is still visible there, as her upper works project from the water.

Spanish–American War

Monitors were used frequently during the Spanish–American War in 1898. Notable United States Navy monitors which fought in the war were USS Amphitrite, USS Puritan, USS Monterey, and USS Terror. These four monitors fought at battles or campaigns such as the Bombardment of San Juan, the Battle of Fajardo, and the Philippines Campaign. Other monitors also participated in the conflict.