At the age of 17, von Hoffman—then a military cadet—disobeyed his mother's wishes and joined the Russian army during the Russo-Japanese War. For actions during the war he was awarded the Order of St. Anna. He participated in World War I, serving in the Russian army, and then under Admiral Kolchak on the White Russian side in the Russian Civil War. Von Hoffman is said by some sources to have been on the Roosevelt-Rondon Scientific Expedition in 1913; however, Theodore Roosevelt does not mention him in his memoir of the expedition, but footage proving von Hoffman's presence can be found here.