The John Ericsson-class ironclads were designed to meet the need of the Swedish and Norwegian Navies for small, shallow-draft armored ships capable of defending their coastal waters.

The standoff between USS Monitor and the much larger CSS Virginia during the Battle of Hampton Roads in early 1862 roused much interest in Sweden in this new type of warship as it seemed ideal for coastal defense duties.

A parliamentary committee set up earlier to investigate the state of the Swedish navy had already concluded that the existing fleet was obsolete and new construction would have to be steam-powered and built of iron.

In response they sent Lieutenant John Christian d'Ailly to the United States to study monitor design and construction under Ericsson.

D'Ailly arrived in July 1862 and toured rolling mills, gun foundries, and visited several different ironclads under construction.

Over time a flying bridge and, later, a full superstructure, was added to each ship between the gun turret and the funnel.

[3] Initially their crew numbered 80 officers and men, but this increased to 104 as the ships were modified with additional weapons.

[2][3] The John Ericsson-class ships had one twin-cylinder vibrating lever steam engines, designed by Ericsson himself, driving a single four-bladed, 3.74-meter (12 ft 3 in) propeller.

The engines produced a total of 380 indicated horsepower (280 kW) which gave the monitors a maximum speed of 6.5 knots (12.0 km/h; 7.5 mph) in calm waters.

[7] Thordön and Tirfing were briefly armed with a pair of 267-millimeter (10.5 in) M/66 smoothbore guns[7] before being rearmed in 1872–73 with two 240-millimeter (9.4 in) M/69 rifled breech loaders, derived from a French design.

[9] The John Ericsson-class ships had a complete waterline armor belt of wrought iron that was 1.8 meters (5 ft 11 in) high and 124 millimeters (4.9 in) thick.

The gun turret's armor consisted of twelve layers of iron, totaling 270 millimeters (10.6 in) in thickness on the first four monitors.

The conning tower was positioned on top of the turret and its sides were ten layers (250 millimeters (9.8 in)) thick.

[2][3] In July 1867 Crown Prince Oscar, later King Oscar II, inspected John Ericsson, Thordön, Tirfing, the steam frigates Thor and Vanadis, and the Norwegian monitor Skorpionen in the Stockholm archipelago before they departed for port visits in Helsingfors, later known as Helsinki, and Kronstadt in August, where they were visited by Grand Duke Konstantin Nikolayevich of Russia, head of the Imperial Russian Navy.

The ship's boilers were replaced by new cylindrical ones that had a working pressure of 5.5 kg/cm2 (539 kPa; 78 psi) and John Ericsson reached 8.17 knots (15.13 km/h; 9.40 mph) on sea trials on 14 May 1901.

[12] The ship was assigned to the Karlskrona local defense force during 1913–18, and she was sold to the Gotland Cement Company (Swedish: Gotländska Kalkstenskompaniet) in November 1919.

The ship ran aground and sank on Lilla Rimö Island, off Norrköping, on 23 July 1883.

The ship was reconstructed at the same time and in a similar manner as was Tordön, except that she received eight 47-millimeter (1.9 in) M/95 quick-firing guns taken from the Komet and Stierna-class torpedo boats.

Tirfing joined her sister Thordön as part of the Göteborg flotilla during World War I and shared her fate.