Wikipedia
An udema ( or ; also udenma) was a type of warship built for the Swedish archipelago fleet in the late 18th and early 19th centuries. It was developed for warfare in the Archipelago Sea in the Baltic and along the coasts of Svealand and Finland against the Russian navy. The udema was designed by the prolific naval architect Fredrik Henrik af Chapman for use in an area of mostly shallow waters and groups of islands and islets that extend from Stockholm all the way to the Gulf of Finland.
The udema was of an innovative new design with a single line of guns along the ship's centerline, a foreshadowing of the dreadnought battleships of the early 20th century. The design proved impractical for its time, however, and only three udemas were built between 1760 and 1776.