MiG-3s were delivered to frontline fighter regiments beginning in the spring of 1941 and were a handful for pilots accustomed to the lower-performance and docile Polikarpov I-152 and I-153 biplanes and the Polikarpov I-16 monoplane. It remained tricky and demanding to fly even after the extensive improvements made over the MiG-1. Many fighter regiments had not kept pace in training pilots to handle the MiG and the rapid pace of deliveries resulted in many units having more MiGs than trained pilots during the German invasion. By 1 June 1941, 1,029 MIG-3s were on strength, but there were only 494 trained pilots.