As the French left Vietnam in 1954, the country was divided to two parts. The southern part (South Vietnam) formed the "Armee de l'air Vietnamienne" and adopted the marking used since 1950 under French supervision which were variations of the national flag, i.e. an orange disc charged with three red thin rings; the national flag was used as rudder marking.
In 1962, the south, now as the Vietnam Air Force adopted a new roundel based on the American one, white star on blue disc and orange bars bordered red and central red line. The rudder marking was the same as before (http://airwar.hihome.com/airwar/vietnam/viet08-a37.jpg.
North Vietnam changed its roundel in 1965 to yellow star on red disc bordered yellow and red bars bordered yellow with no fin flash.
image adapted by Randy Young, 25 April 2016 Source:Wikipedia
On 8 March 1949, after the Élysée Accords1, the State of Vietnam (État du Viêt Nam in Vietnamese, État du Viêt Nam in French), was recognized by France as an independent country ruled by Vietnamese Emperor Bảo Đại. The Vietnamese National Army or Viet Nam National Army (Vietnamese: Quân đội Quốc gia Việt Nam, "National Army of Vietnam," French: Armée Nationale Vietnamienne) was the State of Viet Nam's military force created shortly after that. It was commanded by Vietnamese General Hinh and was loyal to Bảo Đại.2
The Air component of the ANV was the Vietnamiènne Armée de l'Air (VALA, Vietnamese Air Force in English, VNAF) was an Air Department (Branch) within the ANV and later on 1 July 1955 it was established separately as a military force, precursor to the KLVNCH.3 Esteban Rivera, 23 April 2016 Sources: 1 - Wikipedia article 2 - Wikipedia article (in French) 3 - Wikipedia article