In the early 20th century, the term was revived for shallow-draught 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.
[citation needed] It 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.
The wooden walls of Old England cease to exist...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...
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...
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... A storm of cannon-shot damages them no more than a handful of dried peas.
In fact, the thing looked altogether too safe...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.
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.
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.
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.
[citation needed] A late example of a vessel modeled on Monitor was Huáscar, designed by Captain Cowper P. Coles, the advocate and developer of turret ships for the Royal Navy.
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 were reactivated for coastal defence to allay fears about surprise Spanish raids, but this was pure political posturing as the ships were too slow and obsolete to have any military value.
During World War I, the Royal Navy developed several classes of ships which were designed to give close support to troops ashore.
HMS General Wolfe, one of the Lord Clive-class monitors, which had a single 18-inch (457 mm) gun added in 1918, was able to shell a bridge 20 miles (30 km) away near Ostend.
These vessels were among the first to fire on Serbian territory at the start of the First World War, and took part in the bombardment of Belgrade, as well as other Balkan campaigns against Serbia and Romania.
The Italian Navy also constructed some monitors including the Faa di Bruno, using the main gun barrels for the cancelled Francesco Caracciolo-class battleships.
When the requirement for shore support returned, two large new Roberts-class monitors, Roberts and Abercrombie, were constructed and fitted with 15-inch (380 mm) guns from older battleships.
Roberts and Abercrombie were to form part of the British East Indies Fleet in support of Operation Mailfist, the planned liberation of Singapore in late 1945, which was cancelled following the Japanese surrender.
The former Italian WWI monitor Faa di Bruno had been redesignated as floating battery by the beginning of WW2, in which role she continued to play until the capitulation of Italy.
After experiences during WWI, the Russian Civil War and the Manchukuo Imperial Navy raids in the Far East, the Soviets developed a new monitor class for their river flotillas.
Naval Advisory Group in February 1966, and by the summer of 1966 Secretary of Defense Robert S. McNamara authorized the U.S. Navy a Mobile Riverine Force (MRF).
[8] Vietnam Monitors were originally converted from World War II 56-foot (17 m) long all-steel Landing Craft Mechanized (LCM) Mark 6s.
USS Monitor had had very little freeboard so as to bring the mass of the gun turret down, thereby increasing stability and making the boat a smaller and therefore harder target for gunfire.
At the end of the American Civil War, the U.S. Navy Casco-class monitors had large ballast tanks that allowed the vessels to partially submerge during battle.
The British M-class submarines were initially designed for shore bombardment, but their purpose was changed to attacking enemy merchant vessels as their 12-inch (305 mm) gun would be more effective at long range than a torpedo against a moving target.
To overcome the stability problems arising from the heavy turret mounted high in monitors, their hulls were designed to reduce other top weight.