plate. The Coles design required slabs of thickness. This armor could not be produced in any Russian plant, and in Europe, only John Brown & Co in Sheffield, England, was producing armored plate of this thickness and of the required quality. Construction Two of the ships were built by the state-owned New Admiralty yard, the others were ordered from privately owned shipyards. The Galerniy Island yard, Carr and MacPherson and the Nevsky factory (owned by Colonel PF Semyannikov and Retired Lieutenant VA Poletika) each produced two ships. Two ships were prefabricated in Belgium by Cockerill & Co and assembled in Kronstadt. All ships were laid down in late 1863 and launched in 1864. Some of the turrets and steam engines were produced at the Izhorsky Zavod state factory, and some by the Baird Works. Iron armor for the ships was first ordered form John Brown & Co in Sheffield, but they cited difficulties in meeting the demand. Instead most of the 1 inch armor plate needed for the ships was produced by Russian forges. The cost of the Russian-built ships was around 570 thousand rubles for each ship. The two Belgian ships cost 619,000 silver rubles. Armament In their first eight years of operation, the monitors were equipped with three different types of artillery pieces. Procurement efforts for all three types were started at the same time in 1863. An order was placed in 1863 with the Krupp factories in Germany for 9 inch smoothbore guns with steel barrels; these were initially used to arm the monitors. At the same time, Artillery specialist Filemon N. Pestich was sent to America along with Artseulov and Lessovsky to acquire gun technology. He returned in 1864 with technology for the production of 15-inch smoothbore Dahlgren guns, the type in use on the American Passaics. A new gun factory was established in Petrozavodsk in Russian Karelia. Production of Dahlgren guns was immediately started at the Aleksandrovsk gun factory, with the first 15-inch gun cast on 2 January 1864, The first 15-inch guns were installed on the monitors by 1868, but they only became available for all ships in 1869. Unlike on the American sister ships, mixed armaments of 15 inch and smaller guns were not used. Also in 1863 development of a rifled gun started with the help of Krupp technology. The Obukhov State Plant was founded in St. Petersburg to produce guns based