Karl Petrovich Iessen; 30 June 1852 – 30 November 1918) was a Baltic German admiral in the Imperial Russian Navy during the Russo-Japanese War.

Between 1891 and 1893, Jessen was executive officer on the protected cruiser Admiral Kornilov, assigned to the Russian Baltic Fleet and the Far East.

This cruiser squadron conducted commerce raiding and other offensive operations while the remainder of the Russian Pacific Fleet remained bottled in Port Arthur by a Japanese blockade.

However, with the fall of Port Arthur to the Japanese, he played no further offensive role, and concentrated on coastal defense of the region around Vladivostok with his much depleted forces.

[1] After his return to Petrograd, he was reprimanded and faced a court martial, accepting a promotion to the rank of vice admiral and an honorable discharge from the navy in 1908.