Ljung was commissioned as an officer 1944 and was assigned as a second lieutenant to the Swedish Army Signal Troops the same year. He attended the Royal School of Signals in 1950 and the Royal Swedish Army Staff College from 1952 to 1954. Ljung was promoted to captain in the Swedish Army Signal Troops in 1953 and attended the United States Army Command and General Staff College at Fort Leavenworth, Kansas from 1956 to 1957 when he became captain of the General Staff.
