Belgian pilot Charles Van Den Born performed a flying demonstration over
Bangkok in January 1911, greatly impressing Prince
Chakrabongse Bhuvanath, brother of King
Vajiravudh, and he even accepted an invitation for a flight. Chakrabongse sent three army officers to France, who began flight training at
Vélizy-Villacoublay in July 1912. The officers became qualified aviators a year later. Soon after,
Sra Pathum airfield was established along with a temporary hangar to house planes and also host flight training. In late 1913, the three new aviators returned home after arranging for the purchase of four
Nieuport monoplanes and a
Bréguet biplane. The aviation section put on a demonstration in January 1914, gaining the support of the King and a permanent aviation group was established and an air base at
Don Muang was assigned, as the
Royal Aeronautical Service, under Army control. Siam entered
World War I with the
Allies in July 1917, and a
Siamese Expeditionary Force of around 1,200 men was sent to France, arriving in June 1918. Among them were 370 pilots and
groundcrew, including more than 100 officers who were sent to flight school first at Istres and Avord, and then at
Istres,
Le Crotoy,
La Chapelle-la-Reine,
Biscarosse and Piox. Eventually, The 95 pilots who qualified as military aviators flew a few operational
sorties in the closing weeks of the war but suffered no casualties, nor scored any kills. Their training did mean that Siam entered the post-World War I period with one of the best equipped and trained air forces in Asia. In the 1930s the Royal Aeronautical Service began to replace French aircraft with American designs, purchasing more than 95 aircraft, including the
Boeing P-12E,
Curtiss Hawks, and
Vought Corsairs. The air force was formally separated into its own branch, the
Royal Siamese Air Force, in April 1937 and five operational wings were established. In 1939, when Siam became Thailand, the service was renamed the
Royal Thai Air Force. == Structure ==