required the undercarriage to be reinforced and the wing area increased to keep the same wing loading. The M-40F-powered aircraft reached a maximum speed of at . However, the M-40 was not yet ready for service use and the project was cancelled. The aircraft/engine combination did have enough potential that development work continued using the closely related, but more mature, Charomskiy ACh-30B Diesel engine. The cockpit was modified to accommodate two pilots side-by-side and the wing and tailplane areas were increased. The 12.7 mm UBT machine gun in the dorsal turret was replaced by a ShVAK cannon and the nose and ventral ShKAS machine guns were exchanged for 12.7 mm UBT machine guns. Up to of fuel could be carried. The Yer-2/ACh-30B was placed into production at Factory No. 39 in Irkutsk at the end of 1943 and the first production aircraft was submitted to its State acceptance trials the following month. Some excess aircraft were converted as Yer-2ON VIP transports. Operational history The Yer-2 was not in squadron service when Germany invaded on 22 June 1941, but the 420th and 421st Long-Range Bomber Regiments (—DBAP) were formed shortly afterwards. However neither regiment flew any operational missions until later in the summer. On the evening of 10 August Yer-2s of the 420th DBAP, accompanied by Petlyakov Pe-8s of the 432nd DBAP, attempted to bomb Berlin from Pushkino Airfield near Leningrad. The airfield was too short to accommodate a fully loaded Yer-2, but three bombers did manage to take off regardless. 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. Three crews from the 420th DBAP bombed Königsberg during the nights of 28–29 and 30 August – 1 September from Ramenskoye Airport, southeast of Moscow. On 1 October 1941 63 Yer-2s were in service, but only 34 were operational. The 420th DBAP had flown 154 sorties by the beginning of November (6 in August, 81 in September, 67 in October) and had lost 30 of its 40 aircraft. Over half of these (19) were due to non-combat losses. 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. On 4