He served during World World War II against Poland, France and the Soviet Union. Erwin Jaenecke fought in the First World War and started the Second World War as Oberquartiermeister with the 8th Armee in Poland. Later he served in Belgium and France.
On the Eastern Front, he served as commander of the 389th infantry Division and later the IV. Armeekorps.
He was wounded at the Battle of Stalingrad and flown out as one of the last higher officers. In April 1943 he commanded the LXXXII. Armeekorps, and from 25 June the 17th Army in the Caucasus and later the Crimean Peninsula.
In a 29 April 1944 meeting with Adolf Hitler in Berchtesgaden, Jaenecke insisted that Sevastopol should be evacuated and his cut off Army of 235.000 men withdrawn. He was relieved of his command afterward.
Later, he was held responsible for the loss of Crimea, arrested in Romania and court-martialed.
Heinz Guderian was appointed as a special investigator in the case. Guderian proceeded slowly and eventually Jaenecke was quietly acquitted in June 1944. Jaenecke was dismissed from the army on 31 January 1945.
On 15 June 1945 he was arrested by the Soviets and condemned to death.
His sentence was converted to 25 years of hard labor. He was released in 1955 and returned to Germany, after the agreement of Konrad Adenauer with the Soviet Union.