On 1 March 1918, Tadija Sondermajer is transferred to the French elite fighter squadron (GC 12) 'Les Cigognes' ('The Storks') the best fighter plane group in France, it was commanded by celebrated French ace Georges Guynemer, and after Guynemer’s death, by an even greater ace – the legendary Rene Fonck; as one of the 60 top fighter pilots, Tadija was selected to join the group in charge of the hardest combat missions on the Western front during the battle of the Marne. From April 15 to May 21, his group had for enemy the "Flying Circus" composed up of Fokker fighters led by the famous German flying ace Manfred von Richthofen, better known as the Red Baron. During one mission above the enemy line, as he was returning to the base with a empty machine gun, Sondermajer was attacked by three German fighters. He saved himself by performing flying acrobatics, which made the enemy failed to shot down him. On his return from a second fight on May 21 his SPAD XIII caught fire after being shot, miraculously he was able to land in Flanders, Sondermajer survived the crash of his plane but was severely burned with a leg injury. After treatment and demobilization, Sondermajer enrolled at the School of Aeronautics and Mechanical Construction in Paris () where he received a degree in airplane engineering in 1921. In 1923 he left active service to become a reserve officer.