There were a number of foreign customers for the SB. They were mostly satisfied with the aircraft's performance. There were some complaints about the noise, cramped crew compartments, hard undercarriage suspension and in particular about the front gunner's position, which could be reached only through a hatch under the fuselage, preventing the gunner from escaping in the event of a ditching or
belly landing. Czechoslovakia signed an agreement to produce the ANT-40 as Avia B-71.
Spanish Civil War While only 54 SBs had been delivered to the Soviet Air Forces by 1 July 1936, this did not stop the new Tupolev bomber being amongst the first shipments of military equipment sent by the Soviet Union to support the Spanish Republicans when the
Spanish Civil War broke out on 17 July 1936. An initial batch of 31 SBs arrived in
Cartagena aboard the Soviet Freighter
Komsomol in October 1936, flying their first mission, a bombing raid by four SBs against Tablada airfield,
Seville on 28 October. The SBs were used to equip
Grupo 12 of the
Spanish Republican Air Force, which at first was mainly manned by Soviet volunteers and under Soviet control. The SB could outpace the
Fiat CR.32 and
Heinkel He 51 biplane fighters of the nationalist forces, and was therefore difficult to intercept, with dives from high altitude being the only way to intercept the SB. On 29 May 1937 two SBs
attacked the
German pocket battleship Deutschland, mistaking it for the Nationalist cruiser
Canarias, killing 31 and injuring an additional 83 German sailors. In June–July, a second consignment of 31 SBs were received, allowing
Grupo 12 to return to full strength, and a new unit,
Grupo 24, to be established. The delivery of
Messerschmitt Bf 109s to re-equip the German
Condor Legion meant that the SB could no longer evade Nationalist fighters by sheer speed, and losses rose. allowing operations to continue, although losses continued to be high. By the time the Civil War ended in April 1939, 73 SBs had been lost, 40 of them to enemy action. A further 60 SBs were delivered to China in early 1938, these being heavily used to attack Japanese forces during the
Battle of Wuhan. Losses were heavy, forcing the Chinese SB units to be temporarily withdrawn from combat. The Soviet units operating the SB over China re-equipped with the
Ilyushin DB-3 in 1939, allowing their SBs to be transferred to Chinese units, but the Chinese made limited use of these reinforcements. The Soviet Union supplied a further 100 SBs in 1941, just before it signed the
Soviet–Japanese Neutrality Pact. The SB was gradually phased out of front-line operations against the Japanese with the delivery of more modern American bombers from 1942, being partly replaced by
Lockheed Hudsons and
B-25 Mitchells. Limited numbers of SBs continued in non-combat use, including operations against
opium plantations, before being used against the Communists when the
Chinese Civil War flared up in 1945, being finally withdrawn in 1946.
Mongolia , Summer 1939 As well as the aircraft operated by volunteers against the Japanese over China, SBs were used in combat against the Japanese during the
Battle of Lake Khasan on the eastern sector of the
China–Russia border in July–August 1938, one SB being lost. Fighting between Soviet and Japanese forces broke out again at the
Battles of Khalkhin Gol in Eastern Mongolia in May 1939. While SBs were not involved in the May air battles, where the Soviet forces suffered many losses, two Regiments of SBs were deployed to Mongolia in June, flying their first missions on 26 June. SBs were used against Japanese forces when they attacked in early July. The Soviet SB regiments consisted of a mixture of early and later SBs, whose differing speeds caused problems in maintaining formation, while Japanese
Nakajima Ki-27 fighters proved adept in exploiting the poor defensive armament of the SB, with the radio operator operating both the dorsal and ventral guns. SBs continued to be used against the Japanese as the Soviets and Mongolian forces commanded by
Georgy Zhukov carried out a successful offensive until a cease-fire was signed in September 1939.
Winter War On 30 November 1939, the Soviet Union attacked
Finland in the conflict that became known as the
Winter War, with the forces deployed against Finland including several hundred SBs. Losses were heavy, with bomber formations often un-escorted, and forced to operate at low level, where they were vulnerable to Finnish
anti-aircraft fire and fighters. While in 1936 in Spain, the SB could outpace enemy fighters, by now it was vulnerable and poorly armed. SBs were fitted with skis for operation from snow covered airfields, slowing the aircraft and making them more vulnerable, while the need to wear heavy winter clothing made the gunner's job even harder. By the end of the 15-week war, at least 100 SBs had been lost, with the Finns claiming nearly 200 shot down, 92 of them to Finnish fighters.
Eastern Front When
Germany invaded the Soviet Union in June 1941, re-equipment with more modern aircraft such as the
Pe-2 had begun. Still, 94% of the Soviet operational bomber force was equipped with SBs, with 1,500–2,000 SBs deployed along the Western border districts of the Soviet Union. The
Luftwaffe started Operation
Barbarossa with co-ordinated strikes against 66 major Soviet airfields, SBs continued in use for non-combat roles such as supply dropping, glider towing and training, and continued in use in the Far East until 1945. These SBs employed the first air-dropped
depth charges used in combat. Finland lost seven SBs to accidents during the Continuation War, with none being lost in combat, with Finnish SBs claiming three Soviet submarines and a 4,000 ton merchant ship sunk. == Variants ==