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.

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.

[2] 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.

[4] Tirfing, and her sister ship Thordön, were briefly armed with a pair of 267-millimeter (10.5 in) M/66 smoothbore guns[5] before being rearmed in 1873 with two 240-millimeter (9.4 in) M/69 rifled breech loaders, derived from a French design.

[7] 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, totalling 270 millimeters (10.6 in) in thickness on the first four monitors.

That same month Crown Prince Oscar, later King Oscar II, inspected Tirfing, John Ericsson, Thordön, 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.