HSwMS Loke was the fourth, and last, ship of the John Ericsson-class monitors built for the Royal Swedish Navy in the late-1860s.

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.

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] 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.

[6] 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.