The John Ericsson-class monitors were a group of five iron-hulled monitors; four were built for the Royal Swedish Navy and one for the Royal Norwegian Navy in the mid to late 1860s. They were designed under the supervision of the Swedish-born inventor, John Ericsson, and built in Sweden. Generally the monitors were kept in reserve for the majority of the year and were only commissioned for several during the year. The ships made one foreign visit to Russia (visits to Norway did not count as foreign as that country was in a personal union with Sweden) in 1867, but remained in Swedish or Norwegian waters for the rest of their careers. Two of the monitors, Thordon and Mjølner, ran aground, but were salvaged and repaired. Most of the monitors were reconstructed between 1892 and 1905 with more