 Nygren was major at the General Staff in 1912 and was appointed Chief of Staff in the III Army Division in 1912.He was vice chief at the Military Office of the Ministry of Land Defence ("Lantförsvarsdepartementets kommandoexpedition") in 1915 and was lieutenant colonel at the General Staff in 1915.Nygren was appointed head of the Royal Swedish Army Staff College in 1917 and conducted study trips to Germany, Bulgaria, Turkey, the Western Front and the Macedonian front in 1918.