Modern-Aviation

The Tupolev ANT-40, also known by its service name Tupolev SB (Russian: Skorostnoi Bombardirovschik – 'high speed bomber'), and development co-name TsAGI-40, was a high speed twin-engined three-seat monoplane bomber, first flown in 1934. The design was very advanced, but lacked refinement, much to the dismay of crews and maintenance personnel. Numerically the most important bomber in the world in the late 1930s, the SB was the first modern stressed skin aircraft produced in quantity in the Soviet Union and probably the most formidable bomber of the mid-1930s. Many versions saw extensive action in Spain, the Republic of China, Mongolia, Finland and at the beginning of the War against Germany in 1941. Russian crews nicknamed the SB the 'Pterodactyl'.

In 1933 the Soviet Air Force ministry, the VVS set out a proposal for a new fast bomber design capable of at least 300 kph, of reaching and maintaining an altitude of 8,000 meters, and with a minimum range of 700 kilometers carrying a payload not less than 500 kilograms. The Tsentralniy Aerogidrodinamicheskiy Institut (eng:the Central Aerohydrodynamic Institute) (TsAGI) under the chief engineer Aleksandr Arkhangelsky having already been working on this project was quickly able to set about designing this new skorostnoi bombardirovshik (SB) or 'high speed bomber' which would receive the design designation ANT-40. Work on this proposal at TsAGI began in January 1934 and led by A. A. Arkhangelski, two versions were planned – with Wright Cyclone radial engines (ANT-40 RTs), and with the Hispano-Suiza 12Y liquid-cooled V12 engines (ANT-40 IS). The first production aircraft, designated SB, rolled off the production line before the end of 1935, and before ANT-402 had completed its flight test programme. The aircraft entered full production in 1936, and was produced in two plants, State Aircraft Factory No 22 at Moscow and No 125 at Irkutsk until 1941. The aircraft was also progressively fitted with improved engines. At first it was equipped with the Klimov M-100, a license-built version of the Hispano-Suiza 12Ybrs engine, but this was soon replaced by the more powerful M-100A, and from 1938 by the yet more powerful M-103. In an attempt to further improve the performance of the SB, which by 1939 was becoming obsolete, the development of two second-generation versions were authorised, a direct replacement for the SB and a specialised dive bomber.

When Germany invaded the Soviet Union in June 1941, re-equipment with more modern aircraft such as the Petlyakov 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. Upon the onset of Operation Barbarossa, the Luftwaffe raided some 66 Soviet airfields in surprise raids destroying the bulk of the SB's on the ground. Most were either destroyed in these raids, or were destroyed in unescorted low-level attacks against German tanks, where the SB's relatively large size and lack of armour made it highly vulnerable to German light Flak, while German fighters continued to take a heavy toll. As a result, the remaining SB's were relegated to night attacks. By December 1941 almost all of the SBs had either been replaced or lost, although it remained in large-scale use until March 1942 in the North against Finland. 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.
Spanish Civil War.

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. In June–July 1937, 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. Though able to outpace the Fiat CR.32 and Heinkel He 51 biplane fighters, they were easy prey for the new Messerschmitt Bf 109B monoplane fighters. A third and final batch of 31 SBs arrived in June 1938, allowing operations to continue, although losses continued to be high. By the time the Civil War ended in March 1939, 73 SBs had been lost, 40 of them to enemy action.

The Soviet Union signed the Sino-Soviet Non-Aggression Pact on 21 August 1937, and as part of this agreement, supplied large amounts of military equipment to the Chinese Nationalists, as well as deploying complete air force units, nominally manned by Soviet volunteers. An initial delivery of 62 SBs was made in September–October 1937, with combat operations by Soviet forces starting in December with attacks on Japanese ships on the Yangtze River. 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. Finally the Soviet Union supplied a further 100 SBs in 1941, just before it signed the Soviet–Japanese Neutrality Pact. In Northern China, SBs were used in combat against the Japanese during the fighting near Lake Khasan on the border between the Soviet Union and Manchuria in July–August 1938 Fighting between Soviet and Japanese forces broke out again at Khalkhin Gol in Eastern Mongolia in May 1939 where SBs were used heavily against Japanese forces when they attacked in early July. To minimise losses to Japanese fighters, the Soviets changed tactics, flying SB missions at over 6,100 m (20,000 ft) where it was difficult for the Japanese to intercept. SBs continued to be used against the Japanese as the Soviets and Mongolian forces carried out a successful offensive until a cease-fire was signed in September 1939.

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 suffering heavy losses to the small Finnish Air Force claiming some 92 SB's with a furhter 100 or more lost to flak. SBs were fitted 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. Later in the war, many Soviet SBs crashed or force-landed on Finnish soil during the Winter War, with the Finns salvaging as many aircraft as possible, with those in the best condition being sent to Valtion lentokonetehdas for possible repair for use by the Finnish air force. Used also to attack Soviet shipping, these SBs employed the first air-dropped depth charges used in combat sinking three Soviet submarines and a large merchant ship.

Even though the SB was no longer a state of the art aircraft, production continued to increase through 1939 and 1940, as the Soviet Union tried to build up the strength of their air forces to compete with the growing threat of Nazi Germany, with almost 4,000 being built in these two years. The SB was phased out of production in early 1941, being replaced by the Petlyakov Pe-2. There were a number of foreign customers for the SB like Spain and China. They were mostly satisfied with the aircraft's performance, however there were some complaints about the high noise level, cramped crew compartments, hard undercarriage suspension and in particular about the front gunner's position, that could be reached only through a hatch under the fuselage. A total of 6,945 of all variants were built for domestic and export use from factories in Russia and Czechoslovakia.

Operators
Bulgaria - Bulgarian Air Force operated 32 Avia B-71 aircraft redesignated Avia-Katiusza Ě-8.
China - Chinese Nationalist Air Force received 62 SB 2M-100 bombers in the autumn 1937. The Soviet Union delivered 3 more SB 2M-100 and SB 2M-105 bombers from August 1938 – June 1941.
China-Nanjing - The Nanjing regime air force had two Tupolev bombers that had been flown by defected Nationalist pilots.
Czechoslovakia - Czechoslovak Air Force received 60 Russian-built SB with Hispano Suiza 12Ybrs engines in April and May 1938. Another 101 bombers and 60 reconnaissance aircraft were license-built Avia B-71 but only 101 were built.
Finland - Finnish Air Force operated 24 SB bombers. The first eight aircraft (seven powered by M-103 engines, one by M-100 engines) were captured during the Winter War, another 16 aircraft were converted from German-captured material from 5 November 1941 – 27 August 1942. All aircraft were refitted with M-103 engines and were used as anti-submarine aircraft in the LeLv 6 squadron. Two aircraft were rebuilt and were used as trainers. The Finnish Air Force withdrew all SB aircraft in 1945, and all were scrapped in 1950.
Germany - Luftwaffe operated captured aircraft, Czech-built Avia B-71 and Soviet SB.
Poland - Polish Air Force operated few USB 2M-103 aircraft for training after World War II.
Slovakia - Slovak Air Force operated one Avia B-71 aircraft until April 18, 1943, when čtk Anton Vanko and four other airmen defected with it to Turkey.
Soviet Union - Soviet Air Force. Aeroflot received an unknown number of retired military SB 2M-100 aircraft in 1938 and after rebuild, used them under the designation PS-40. Another batch of retired SBbis 3 bombers was rebuilt in 1940 and used under the designation PS-41.
Spanish Republic - Republican Spanish Air Force received its first 31 SB 2M-100A bombers on 14 October 1936. The second batch of 31 aircraft was delivered in June–July 1937 and a final batch of 31 following in 1938. The Soviet Union delivered a total of 93 SBs to Spain.
Spanish State - Nationalist Spanish Air Force captured 19 SB 2M-100A bombers. All were overhauled and Soviet M-100 engines were replaced with French Hispano Suiza 12Ybrs. These aircraft were used operationally and later for training duties, and were retired in 1950. Spanish pilots called captured SB bombers Katiuska.