SMS Hansa  was a German ironclad warship built in 1868–1875. She was the first ironclad built in Germany; all previous German ironclads had been built in foreign shipyards. She was named after the Hanseatic League, known in Germany simply as Hanse, Latinized Hansa. The ship was launched in October 1872 and commissioned into the German Imperial Navy in May 1875. Designed as for coastal bombardment, Hansa was classed as an armored corvette and armed with eight 21 cm (8.3 in) guns in a central battery.

The 21 cm RK L/19 was the later name of a rifled breech loader gun of the Prussian Navy. This gun started with a massive gun barrel, cast from steel in one piece. In 1868 a built-up gun barrel version was tested in Prussia and found to be much more powerful. Many of the massive guns were then changed to built-up guns. These changed guns became known as kurze Ring Kanone, and later as 21 cm Ring Kanone L/19.