HNoMS Mjølner was the fourth of five ships of the John Ericsson-class monitors built for the Royal Swedish Navy and the Royal Norwegian Navy in the mid-1860s. Impressed by the use of ironclads during the American Civil War, the design was based on that of the USS Monitor. 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.