At the start of the Winter War with the Soviet Union (the Finnish-Soviet War of 1939–1940), Heinrichs commanded III Corps and helped to stop the invading Red Army at Taipale. In February 1940, Heinrichs took command of the Karelian Army and liberated the Karelia-Ladoga region. The next month he was promoted to commander of Finnish land forces. In January 1942, Heinrichs was promoted to chief of the General Staff for the Continuation War (the resumption of fighting with the Soviet Union that lasted until 1944). In 1944, Heinrichs was awarded the Mannerheim Cross and promoted to general of infantry.
In August 1944, Marshal Carl G. Mannerheim became president of Finland. At the end of 1944, he gave Heinrichs complete charge of military affairs and the title of commander in chief of Finnish armed forces. He served in that post for less than a year before being forced to resign in the summer of 1945, accused of being involved in hiding significant weaponry and creating an organization for guerrilla war as part of the "underground defense policy" immediately after the war.
Heinrichs then resumed his writing. Closely associated with Mannerheim, he was the ghostwriter for the marshal's memoirs covering the Civil War, the 1930s, and the Continuation War. Heinrichs also wrote two books on the Napoleonic wars. Heinrichs died at Helsinki, Finland, on 16 November 1965.
Spencer E. Robbins III
Upton, A. F. Finland in Crisis 1940–1941. Ithaca, NY: Cornell University Press, 1964.; Warner, Oliver. Marshal Mannerheim and The Finns. Helsinki: Otava Publishing Co., 1967.