Gabriel Voisin was greatly affected by the death of his brother Charles Voisin in 1912 in an automobile accident near Belleville-sur-Saône, but he continued the expansion of the Boulogne-Billancourt factory, under the changed name Société Anonyme des Aéroplanes G. Voisin.
After 1912, the factory shifted its manufacturing and sales towards supplying the French military. When World War I broke out in 1914, Gabriel Voisin immediately volunteered for service with French air corps. The Voisin III, a two-seater pusher biplane with a 120 hp Salmson radial engine, was extensively used for bombing and observation missions during World War I. It had a light steel frame and thus could be stationed outdoors. The Voisin III was built in large numbers (about 1,000) between 1914 and 1916 and sold not only to the French air services but also to other allies, including Russia. The Type VIII (about 1,100 built) and Type X (about 900 built) were delivered in 1917 and 1918. Those last to appear Voisin military aircraft were almost identical in appearance to the Voisin III, although they were heavier and featured twice as powerful Peugeot and Renault engines. They also had a longer range and carried almost twice the bomb load of their predecessor. A complete and original Voisin Type VIII bomber aircraft is preserved in excellent condition at the Smithsonian's National Air and Space Museum in Washington,D.C. It is the oldest preserved bomber aircraft in the world.