SMS Prinz Adalbert  was an ironclad warship of the Prussian Navy and later the Imperial fleet. She was built in Bordeaux, France in 1864 for the Confederate States Navy. Prussia bought her during the Second Schleswig War against Denmark, but she was not delivered until after the war. She was designed as an armored ram but also carried three guns: one 21 cm (8.3 in) and two 17 cm (6.7 in) pieces in armored turrets. She was named after Prince Adalbert of Prussia, an early proponent of Prussian naval power.

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.