Gilsher studied civil engineering before entering the Nikoliavsky Cavalry school on December 13, 1914. On August 29, 1915, he transferred to the air service, first attending flight school at Gatchina before going to the front with the newly formed 4th Army Air Detachment on November 19, 1915. A few weeks later, an accident with a propellor blade injured his left hand. When he recovered, Gilsher completed advanced flight training at Odessa, then returned to the front on April 5, 1916.

Promoted to Cornet (Cavalry Second Lieutenant), he was attached to the newly formed 7th Fighter Detachment. Crashing a badly damaged Sikorsky S-16 on May 9, 1916, Gilsher's left leg had to be amputated. Refusing to give up his flying career, he learned to use a prosthesis, returned to his squadron as temporary commander and continued flying combat missions. Flying the Nieuport 21, he was credited with five victories before he was killed in action by enemy fire.