Rhein - class monitor The " Rhein " class of ironclad riverine monitors ( " Flußkanonenboote " ) were a pair of ships built by the German Imperial Navy in the aftermath of the Franco - Prussian War . The class comprised two ships , " Rhein " and " Mosel " ; both were built by the AG Weser shipyard in Bremen , in 1872 – 1874 . They were armed with a pair of bronze cannon in a revolving gun turret . The ships were intended to protect the German border with France in the event of a conflict , but had short service lives , as war did not come . They served briefly in the defenses of Coblenz , starting in 1875 , before being withdraw from service . The two ships were sold for scrap , apparently in December 1884 . Design . " Rhein " and " Mosel " were long at the waterline and long overall , and had a beam of . At cruising load , the monitors had a forward draft of , an aft draft of , and a maximum draft of . Freeboard was forward and aft . The ships were designed to partially flood for combat , which would submerge the hull so only the upper casemate and gun turret would be above water . This reduced the freeboard to and , respectively . The ships had a designed displacement of , and at full load they displaced . The hulls were constructed with transverse iron frames . The ships had a crew of one officer and twenty - two enlisted men , and both carried a single boat . The ships were powered by two horizontal 2 - cylinder single - expansion steam engines ; these drove a pair of 3 - bladed screws on diameter . The engines were placed in a single engine room . Two locomotive boilers with two fireboxes apiece supplied steam to the engines ; they were located in a separate boiler room . The engines were rated at and a top speed of . In service , they were capable of 48 nominal horsepower and . The ships maneuvered slowly and turned poorly , especially steaming downstream . They did not handle well upstream either , particularly in turning against the current . Handling while the ships were flooded for combat was especially dangerous . The ships were each armed with a pair of L / 19 bronze cannon manufactured by Krupp ; they were rifled , muzzle - loading guns , mounted in a single revolving gun turret placed on an armored casemate amidships . The guns fired a 36 - pound shot , and were supplied with 300 rounds of ammunition . The ships were protected with a combination of wrought iron armor and teak . The turret sides were armored with of iron , backed with of teak ; the roofs were thick . The conning tower had thick sides and a thick roof . The casemate was protected with 65 mm of armor plate on the sides . Service history . The intention for " Rhein " and " Mosel " was to use them to defend the railway bridges on the Rhine in the event of a French war of revenge after the Franco - Prussian War in 1870 – 1871 . The ships were both built at the AG Weser dockyard in Bremen , under construction numbers 23 and 24 , respectively . The Rhine Railway Company was compelled to contribute 300 , 000 Thaler s to the construction of the ships , as they were intended to defend the railway bridges the company used at Rheinhausen . Both ships were laid down in 1872 and launched later that year ; they were both commissioned into the Imperial Navy on 25 April 1874 . They spent the first year of their career at Rheinhausen , until 7 April 1875 , when they were transferred to the defenses of Coblenz . By the time the two monitors entered service , the prospect of a French attack had decreased , prompting the Navy to question the usefulness of retaining the vessels . As a result , they were quickly removed from service . The ultimate fate of the two ships is unclear ; according to naval historian Erich Gröner , both ships were sold for 3 , 500 gold marks in December 1875 . Robert Gardiner , however , states that the ships remained , out of service , until 1884 , when they were sold for scrapping . The latter version would appear to be correct , as J . F . von Kronenfels published an elevation and deckplan of " Rhein " in 1881 , with the inference that " Rhein " and " Mosel " were still extant at that time .