Designed by V. G. Yermolayev, previously a member of the design team concerned with the STAL series of aircraft, the DB-240 long-range bomber prototype was flown for the first time in June 1940. A second prototype followed in September , by which time preparations for mass production at Voronezh were in hand, but the German invasion led to evacuation of the factory in July 1941, by which time 128 examples of the DB-240 had been delivered under the designation Yermolayev Yer-2.

An all-metal mid-wing monoplane of inverted gull-wing configuration and with a twin fin-and-rudder tail unit, the Yer-2 had tail-wheel landing gear, the main units retracting into the nacelles of its two M-105 engines; accommodation was provided for a crew of four.

By the autumn of 1941 the Yer-2 was in action with two air regiments, making attacks as far distant as Berlin and Konigsberg, but the need for increased range led to experiments with AM-35 engines (April 1942 ) and a modified wing. Following tests with Charomsky diesels, a new version with ACh-30B engines was approved for production in December 1943 at the Yer-2 factory, which was then established in Siberia. Some 300 examples of the Yer-2/ACh-30B were built, forming the backbone of the Soviet long-range bombing force; they also incorporated some improvements, including a revised cockpit, a larger-calibre machine-gun in the ventral position and an enlarged bomb bay accommodating three 1000kg bombs. Maximum speed of this version was 446km/h and its range 5000km, but despite this capability most Yer-2 operations were of necessity carried out at short range on targets behind the front line.