Although designed as a long-range medium bomber it was flown on tactical ground-attack missions during the Battle of Moscow with heavy losses.

[1][2] Roberto Bartini had designed and built the Stal-7 airliner whilst he was the chief designer at the ZOK NII GVF (Russian: Завод Опытных Конструкций Научно-Исследовательского Института Граждаского Воздушного Флота – Zavod Opytnykh Konstrooktsiy Naoochno-Issledovatel'skogo Institoota Grazhdanskogo Vozdooshnogo Flota, lit.

[3] During flight trials with maximum all-up weight the prototype crashed on takeoff in early 1938, resulting in the arrest of Bartini and his imprisonment in a Siberian Gulag in February 1938.

After repair the Stal-7 carried on with the flight-test programme, including a record-breaking nonstop flight on 28 August 1939 when it flew Moscow—Sverdlovsk—Sevastopol—Moscow; a distance of 5,086 km (3,160 mi) at an average speed of 405 km/h (252 mph).

The pilot's cockpit was offset to port to improve his downward view and the navigator/bomb aimer sat in the extensively glazed nose with a 7.62-millimeter (0.300 in) ShKAS machine gun, the radio operator sat below and to starboard of the pilot and the dorsal gunner in a partially retractable turret with one 12.7-millimeter (0.50 in) Berezin UBT machine gun.

Its defensive armament was deemed inadequate and other problems included an excessively long take-off run and engine defects.

[6] A Yer-2 was modified with experimental Mikulin AM-37 engines, a reinforced undercarriage, armored seats for the navigator and gunner, and 12.7 mm UBT machine guns in place of its original ShKAS weapons.

It first flew in July 1941 and was able to reach 505 km/h (314 mph) at 6,000 m (19,685 ft), but the range was reduced to 3,500 km (2,175 mi) carrying 1,000 kg (2,205 lb) of bombs.

[7] The engine was unreliable, however, and had cooling problems that the Mikulin OKB did not have the resources to resolve so it was cancelled in October when the factory was forced to evacuate from Moscow by the German advance.

[9] The Yer-2 was not in squadron service when Germany invaded on 22 June 1941, but the 420th and 421st Long-Range Bomber Regiments (Russian: Dahl'niy Bombardirovchnyy Aviapolk—DBAP) were formed shortly afterwards.

Two managed to bomb Berlin, or its outskirts, but only one successfully returned; the other was shot down by 'friendly' Polikarpov I-16s when it reentered Soviet airspace and the third aircraft went missing.

Losses were extremely high over the autumn and winter as they were inappropriately committed against German tactical frontline targets during the Battle of Moscow at low altitudes and only 12 were in service on 18 March 1942.

[12] The first combat mission undertaken by Yer-2s after they returned to production was a raid on Königsberg on 7 April 1945 by the 327th and 329th Bomber Aviation Regiments (Russian: Bombardirovchnyy Aviatsionyy Polk).