 By July, nine Bf 110 and three Bf 109 fighter "Staffeln" (squadrons) were equipped with the new engines, By the end of October around 1,200 DB 601N engines had been delivered.and the number of aircraft equipped with the improved engine gradually increased through the second half of the year.However, due to leaking valves there was relatively high wear on the 601N-engines, which had a life of about 40 hours.