 By the end of 1934 most of the Polikarpov I-3s and Tupolev I-4s had been replaced and deliveries had begun to Naval Aviation.The I-5 began to be replaced by the Polikarpov I-15 in 1936, and was completely phased out from front-line use by the end of 1937, but continued to be employed as an advanced trainer.Following the German Invasion of the Soviet Union in June 1941, the heavy losses of front-line aircraft endured by the VVS together with the disruption of aircraft production resulted in I-5s being removed from training units and returned to combat service as ground-attack aircraft or night bombers until early 1942.