Flying Regiment 4 ( or LeR 4) was a bomber aircraft regiment of the Finnish Air Force. The regiment was formed on January 1, 1938 and was active during the Winter War, the Continuation War, and the Lapland War. During the Winter War, the unit flew 423 war missions, of which 22 were strategic and photo reconnaissance flights with its Bristol Blenheim Mk.Is. 18 aircraft and 21 crew members were lost. During the Lapland War LeR 4 flew 462 missions against the Germans, losing 7 aircraft and 16 crew members.