Complex sentence: Shortly after the war Häyhä was promoted from alikersantti (corporal) extraordinarily to Vänrikki (Second Lieutenant) by Field Marshal Carl Gustaf Emil Mannerheim; no one else has gained rank so quickly in Finland's military history.
Split into simpler sentences: Shortly after the war, Häyhä was promoted from Alikersantti (Corporal) to Vänrikki (Second Lieutenant) by Field Marshal Carl Gustaf Emil Mannerheim. No-one else has gained rank so quickly in Finland's military history.