HNoMS Mjølner ( 1868 ) HNoMS " Mjølner " was the fourth of five ships of the s built for the Royal Swedish Navy and the Royal Norwegian Navy in the mid - 1860s . Impressed by the use of ironclad s during the American Civil War , the design was based on that of the . They were designed under the supervision of the Swedish - born inventor , John Ericsson — coincidentally , designer of the " Monitor " — , and built in Sweden . " Mjølner " was delivered in 1868 and ran aground the following year , although she was not seriously damaged . The ship was reconstructed in 1897 and given modern breech - loading guns . " Mjølner " was sold for scrap in 1909 . Design and description . The " John Ericsson " - class ironclad s 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 the and the much larger 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 . John Ericsson , designer and builder of the " Monitor " , born in Sweden — although becoming an American citizen in 1848 — offered to share his design with the Swedes . 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 . He returned to Sweden in 1863 having completed the drawings of a " Monitor " - type ship under Ericsson ' s supervision . The ship measured long overall , with a beam of . She had a draft of and displaced . " Mjølner " was divided into nine main compartments by eight watertight bulkheads . Over time a flying bridge and , later , a full superstructure , was added to each ship between the gun turret and the funnel . Initially her crew numbered 80 officers and men , but this increased to 104 as she was modified with additional weapons . Propulsion . The " John Ericsson " - class ships had one twin - cylinder vibrating lever steam engines , designed by Ericsson himself , driving a single four - bladed , propeller . Their engines were powered by four fire - tube boiler s at a working pressure of . The engines produced a total of which gave the monitors a maximum speed of in calm waters . The ships carried of coal , enough for six day ' s steaming . Armament . " Mjølner " was armed with a pair of Armstrong rifled muzzle - loading guns . Each gun was constructed of steel and weighed . The ship also carried a gun . During " Mjølner " s reconstruction in 1897 her gun turret was fixed in place and modified to serve as a barbette for her two new breech - loading Cockerill guns . She also received two and Cockerill guns mounted in her superstructure . In addition two Hotchkiss 5 - barrel revolving guns were mounted in the superstructure . They fired a shell weighing about at a muzzle velocity of about . This gave them a range of about . They had a rate of fire of about 30 rounds per minute Armor . The " John Ericsson " - class ships had a complete waterline armor belt of wrought iron that was high and thick . The armor consisted of five plates backed by of wood . The lower edge of this belt was thick as it was only three plates thick . The maximum thickness of the armored deck was in two layers . The gun turret ' s armor consisted of twelve layers of iron , totalling in thickness on the first four monitors . The inside of the turret was lined with mattresses to catch splinters . The base of the turret was protected with a glacis , high , and the turret ' s roof was 127 millimeters thick . The conning tower was positioned on top of the turret and its sides were ten layers ( ) thick . The funnel was protected by six layers of armor with a total thickness of up to half its height . Service . The Norwegians had built one monitor - type ship of their own , , in 1865 , and laid down several others , but the Norwegian Parliament authorized construction of " Mjølner " in 1867 in Sweden at the cost of 1 , 102 , 000 Norwegian krone . She was launched in 1868 and completed on 7 September of that year . The ship ran aground at Kragerø on 21 June 1869 . " Mjølner " could not be pulled off the rocks until the ship ' s ammunition , iron ballast and of coal were removed . Her repairs were completed on 7 July 1869 by the Royal Dockyard at Horten , at the cost of 5 , 000 krone . The court of inquiry found the ship ' s commander and the pilot liable for the repairs , but the parliament released the two from their obligation two years later . She was visited by King Charles XV of Sweden on one occasion when visiting one of Sweden ' s west - coast ports in the early 1870s . " Mjølner " was laid up after her refit in 1897 , but was mobilized during 1905 when the personal union between Sweden and Norway was dissolved . She returned to reserve afterward before being sold for scrap in 1909 .