Both these ships were being built for the Russians in 1854 by Pitcher of Northfleet, on the Thames, when they were confiscated and instead commissioned for the Navy as a consequence of the Crimean War. They are of the same design, both were wooden screw corvettes of 1296 tons, 195 x 39 ft, but have different armament. The 'Cossack' (ex-'Witjas) mounted twenty 8-inch guns: the 'Tartar' (ex-'Wojn') mounted two 110-pdrs, four 40-pdrs and fourteen 8-inch. They were launched within two days of each other on 15 and 17 May 1854 and were eventually broken up by Castle's at Charlton, also on the Thames, 'Tartar' in 1866 and 'Cossack' in 1875. Some of 'Cossack's' Baltic service is visually recorded in the Baltic album of Captain (late Admiral Sir) Edward Gennys Fanshawe who commanded her there in 1855-56 (PAI4673 and following).