Karl Lennart Oesch (8 August 1892 – 28 March 1978) was one of Finland's leading generals during World War II.

As a member of the Royal Prussian 27th Jäger Battalion, he fought on the German side of World War I on the Eastern Front, participating in combat in the region of Misa.

[1] Oesch's battalion saw action especially in the area of the Rautu railway station, which was held by the Finnish Reds who were supported by an armored train.

Later that year, he took command of the Guards Jaeger Battalion (Finnish: Kaartin jääkäripataljoona), a position he would hold until 1920.

Once he had returned to Finland, Oesch commanded the newly created general staff academy Sotakorkeakoulu.

Oesch also served briefly as Deputy Minister of the Interior Affairs from 3 to 14 March 1932, during the crisis caused by the Mäntsälä rebellion.

[1] In early March 1940, just prior to the end of the Winter War, Oesch was given command of the Coast Group, whose sector along the Bay of Viipuri had become critical.

Oesch replaced Major General Kurt Martti Wallenius, who had taken command only three days prior.

[1] According to Robert Edwards, Wallenius had "retreated to his command post and became very drunk" after losing his nerve from the intensity of the combat.

[5] Following the end of the war, Oesch first returned to his previous post as the Chief of the General Staff for a few weeks, before taking the command of II Corps.

[1] Following Finno-German negotiations that had been ongoing from at least May 1941, the Finns mobilized on 10 June 1941 in preparation for the Continuation War, the Finnish component of the German invasion of the Soviet Union.

[8] Consisting of the 4th, 8th, 10th and 12th divisions,[9] it was initially tasked with the defense of the southernmost sector of the Finno-Soviet border on the shore of the Gulf of Finland.

[19] On the morning of 14 June 1944, Oesch received a call from Lieutenant General Aksel Airo with the following message:[20] Everything's going to hell on the Isthmus.

[30] After Oesch was released from prison in 1948, he devoted himself to military history, researching and writing extensively on Finnish experiences in World War II.