Tupolev SB in Soviet Service. Part Seven.

 

The SB continued to serve during World War 2, specially during the siege of Leningrad and the Battle of Moscow, as we've already stated, but it was also, numerically speaking, the most important bomber the VVS had in the Stalingrad region when the Axis forces launched their offensive against the Caucasus in June 1942. 

The SB in all its variants served, in some sectors, in the night bomber role well until 1943, even if they were being replaced by either the Tupolev Tu-2 or the Petlyakov Pe-2 when they became available. The SBs were also used in other secondary roles by the VVS like supply-dropping, glider-towing, training and transport in the Far East until the end of the war in 1945.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

Tupolev SB in Soviet Service. Part Four.

 

The Tupolev PS-41 was a civilian version of the SB 2M-103. It was developed by Aeroflot in 1939 and by December 1940 forty-nine machines were in service. As civilianized as it was, every defensive armament, as well as armour plating and bomb release systems were deleted, with the exception of the cartridge case ejector tunnel, which remained in the nose. Many PS-41s had an additional antenna mast placed in front of the canopy frame. When serving with Aeroflot, most of them were left in bare metal with civil registration codes and Aeroflot's logo (albeit not always present), painted in black.

From early 1940 onwards, many PS-41s were assigned to Aviaarktika (Aeroflot's Polar Aviation Division). This organization served in the USSR's most northern region under extreme conditions, hence the non-retractable ski undercarriage the PS-41 were equipped with. Most of them were painted in orange or had their noses or engine cowlings painted red to increase their visibility. 

Shortly after the German Invasion of the USSR in June 1941, Aeroflot's PS-41 were pushed into service with the Civil Air Fleet (GVF in Russian acronym) under VVS (Soviet Air Force) command. Some PS-41s were assigned to liaison squadrons, operating from bases in Moscow and northern USSR. They were used for liaison duties between the Central Military Headquarter in Moscow and the Transcaucasian Front. They were also employed as liaison to link Moscow with the newly established industrial centers east of the Ural mountains. 

In combat, the PS-41 was also used, taking advantage of its high speed, to resupply beleaguered Soviet defenses in the Leningrad area, to supply the city with mail, medicines and military staff. 

As more modern Soviet bombers as the Tupolev Tu-2 or the Petlyakov Pe-2 became available, some former SB 2M-103 bombers were converted to PS-41 standard and assigned to GVF, to ease the acute shortage of transport planes the VVS suffered all along World War 2. 

Overall, the PS-41 served well and became VVS' main high speed transport during the war. It was kept on service for a short period of time after the conflict, until it was gradually replaced by more modern types like the Ilyushin Il-12 or the Lisunov Li-2.

There was an extended range sub-variant, called PS-41 bis designed for mail transport. It featured a pair of external wing mounted fuel depots in lieu of the bomb racks. Those depots allowed for an increased range of 1.180 km (733 miles). 

The Tupolev SB-RK was a regular SB 2M-100A fitted with two Klimov M-105R engines. This served as the initial prototype for the ground attack variant of the SB which eventually became the Arkhangelsky Ar-2. 
The Tupolev SBB was an attempt made by Arkhangelsky to modernize the SB design. It featured smaller wings and an almost complete new redesign with twin tail. The only prototype flew for the first time in September 1940. It was tested against the Pe-2 prototype and the Yakovlev Yak-4 and was discarded due to unsatisfactory performance. Some few attempts were made to attract VVS' attention on the type but the interest was lost.

There was another test aircraft based on the frame of the Tupolev SB. Igor P. Tolstikh an engineer from TsAGI (Central Aero and Hydrodynamics Institute) led a team to investigate a tricycle undercarriage (based on implanting a nose-wheel) in 1940. This landing gear configuration, however, wasn't new in the USSR as another aircraft, Kharkov KhAI-4 employed a nose-wheel back in 1934. 
A heavily modified SB 2M-103 was the basis for the nose-wheel arrangement. This experiment was never intended to be put into mass production, as it was just an study to improve future Soviet bombers.
The nose section was heavily modified to incorporate a large nose-wheel with two bracing struts. The main non-retractable undercarriage was repositioned to the rear.
It was test flown by the famous Soviet test pilot Marc L. Gallai on taxiing and landing flights, who praised the new arrangement as it made it much easier to take off and land, than the conventional tail-wheel bombers. 
TsAGI's prototype, nicknamed as 'Pterodactyl', was assigned to the NII (Flight Research Institute) located at Kratovo, near Moscow, in late 1940. Tests continued until 1941, when Germany launched Operation Barbarossa, invading the USSR in June. The first Soviet bombers with tricycle landing gear arrangement, didn't see the light until after the end of the war, namely the Tupolev Tu-12. 

Sources:

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/prototypes/SBB.htm

Tupolev SB in Soviet Service. Part Two.

 

The first combat usage of the Tupolev SB under VVS's (Soviet Air Force) Red Star was in the Battle of Lake Khasan. This battle was part of the many Soviet-Japanese border clashes in the eastern sector of the Sino-Soviet Manchurian region which took place between 29th July and 11th August 1938. One Tupolev SB was lost to Japanese fire. 

Tensions escalated in the region and fighting broke out again in the Khalkin Gol, eastern Mongolia, close to the border with China, in May 1939. At first there were two SBAP (Russian acronym for 'Fast Bomber Regiment') units present; 150 and 38 SBAP. 

In this battle, which lasted until 16th September and caused Soviet forces heavy losses, the SBs were not involved at first. However, due to the increasing Soviet casualties, two regiments of SB bombers were deployed in June, flying their first mission of the 26th. The SBs were employed thoroughly when the Japanese launched an attack in early July. 

Both 150 and 38 SBAPs were composed of a mixture of old and new models of the SB, so the differing speeds between bombers proved to be a serious problem when maintaining formation, specially when the Japanese Nakajima Ki-27 fighter attacked and the poor defensive arrangement of the SB could do little to defend, as the radio operator had to man both dorsal and ventral turrets. In order to minimise casualties against Japanese fighters, Soviets changed their tactics, so the SBs had to fly in altitudes over 6.100 m (20.000 ft), where it was difficult for the Japanese to intercept. In August a new regiment, 49 SBAP arrived in the battlefield and the SBs were employed in aerial raids against Japanese forces until Soviet and Mongolian forces lead by Georgy Zhukov carried out an offensive which ended with the cease-fire in 16th September 1939.

The SB was also employed by the VVS in the Soviet Invasion of Poland. At 6:00 am, on 17th September 1939 approximately 310.000 Soviet troops crossed the Polish border from the east and the SB was the backbone of the VVS during this campaign. Both Belarussian and Ukrainian fronts had a total of 637 SB 2M-100As available when the Polish-Soviet War broke out. They were assigned to 10th, 16th, 18th and 70th SBAPs. 

During the first days of the invasion, most of their missions were against strategical railroad stations and communication hubs, including the Stanislawow and Buczacz marshalling yards, as well as Polish airfields of Kowel, Dubno and Luzk, where they encountered resistance and Polish P-11 fighters shot down two SBs that day.

On 19th September, some of the remaining P-11s tried to attack a formation of SBs without any success at all. 

The SBs also raided one of the last Polish strongholds near Kamien Koszyrski on 22nd September. By that date the Polish Air Force had already collapsed and the VVS only flew some sporadic sorties over Poland. On 29th September a formation of various SB 2M-100As bombed the town of Nujno. 

VVS's bombing operations over Poland were limited until 6th October 1939, when the Polish campaign ended. This was because of the lack of suitable targets and only a handful of SBs were lost in the 20 days this campaign lasted.

The Tupolev PS-40 was a civilian transport variant, which we will cover in a future post. 

The Tupolev MMN was an version which featured several aerodynamical improvements. It was made on the basis of the SB 2M-103 and was powered by two 1.100 hp Klimov M-105 engines. Each engine, housed in an aerodynamically modified cowling was equipped with a centrifugal two-speed twin-stage supercharger driving a three-bladed propeller. 

The wingspan was reduced and the tail was redesigned and reduced in size. Nose section was also modified in order to have clearer portions. Armament consisted on two 7,62 mm ShKAS machine guns placed in a dorsal turret and a single ShKAS machine gun in the nose section. This reduced the defensive armament of the regular SB as they normally had two ShKAS in the nose.

The MMN also featured additional wing fuel tanks and a second landing light. It was also lighter than the SB 2M-013. 

It was accepted for state trials in September 1939 and achieved a top speed of 458 km/h (285 mph) flying at 4.200 m (13.780 ft). This was only 8 km/h (5 mph) faster than the standard SB 2M-103. As it had smaller wings, it also had smaller wing area, resulting in a faster landing speed of 160 km/h (99 mph), making it more dangerous. The MMN did not pass state trials because of its nimble defensive armament, its marginal faster speed and its high landing speed over the SB 2M-103. The only prototype was assigned to Aeroflot where it received the nickname of Shchuka (Pike).

Sources:

1st https://en.wikipedia.org/wiki/Tupolev_SB

2nd https://en.wikipedia.org/wiki/Battle_of_Lake_Khasan

3rd https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol

4th https://j-aircraft.com/research/George_Mellinger/sovietorderofbattle.htm

5th Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

6th https://en.wikipedia.org/wiki/Soviet_invasion_of_Poland

7th http://www.airvectors.net/avtu2.html

Tupolev SB in Soviet service. Part one.

 

The Tupolev SB (development TsAGI-40), was a Soviet high-speed bomber, twin-engined, three-seat monoplane bomber which flew for the first time in 1934. 

Its inception can be traced to the Tupolev ANT-40, studies of which began in early 1930s with speed given very high priority, as it was considered the best defence against fighters. 

In 1933 UVVS (Soviet Air Ministry) issued a requirement. In January 1934, TsAGI (Central Aerodynamic Institute) had gathered enough information to make that project real. 

The SB was developed at Tupolev KB (design bureau) by a team led by Aleksandr Arkhangelski. 

There were two versions planned, one powered by the Wright-Cyclone radial engine (called ANT-40RT) and another powered by the Hispano-Suiza 12Y liquid-cooled V-12 engine (called ANT-40IS). The experience gained with the design of the ANT-21 heavy fighter was put into practice.

The first prototype, ANT-40.1RT (Wright powered) made its first flight on 7th October 1934, while the second one ANT-40.2IS (Hispano-Suiza powered) flew on 30th December 1934 and showed superior performance. The Hispano-Suiza variant was actually a Klimov M-100, which was the Soviet copy of the Hispano-Suiza 12Y engine.

The ANT-40.2 was considered for production thanks to its good performance numbers for the time. However, it had consistent teething problems which lead to unhappy personnel to cover it with placards, listing its defects before the visit of Sergo Ordzhonikidze (Soviet commissar for heavy industry). When seeing those placards, Ordzhonikidze summoned Tupolev to a meeting at the Kremlin to discuss those shortfalls. In that meeting, Tupolev stated that those defects were trivial, to which Stalin answered:

"There are no trivialities in aviation; everything is serious and any uncorrected 'triviality' could lead to the loss of an aircraft and its crew.".

The first production aircraft was completed before the end of 1935 (when the ANT-40.2 was still under testing) and it entered full production in 1936. It was manufactured in two plants. Plant No 22 at Moscow and plant No 125 at Irkutsk (Siberia) from 1937 until 1941. 

As stated, there was a second prototype of the ANT-40IS, called ANT-40IS 2. It featured various improvements such as enlarged tail unit, engine nacelles moved slightly forward and a trim tab added to the right aileron. This prototype was tested with a fixed ski landing gear and defensive armament installed (a 7.62 mm ShKAS machine gun in the rear cockpit). After testing of this second prototype was completed, it was sent to plant No 22 to incorporate such improvements into production aircraft.

The ANT-46 was a heavy-fighter variant, directly derived from the ANT-40.1RT but powered by two French Gnome-Rhône 14K radial engines rated at 800 hp each. It was armed with two 76 mm APK-4 recoilless guns placed in the outer wings. It was also equipped with two fixed rearward-firing 7.62 mm ShKAS machine guns installed in the inner part of each wing. They were controlled from the gunner cockpit, who was also provided with the usual ShKAS in his cockpit that every SB had. 

There was also provision (although it was never installed) for a 12,7 ShVAK machine gun placed in the nose. 

In November 1934 the project received the ANT-46 denomination from Tupolev and the official DI-8 denomination from Soviet authorities. 
The prototype of this variant was completed in the summer of 1935 and flew for the first time in August 1935. During winter 1935-1936 it was tested with a ski landing gear and the engine cowling was changed.

It was tested by Tupolev KB until June 1936. Those tests revealed stability problems, for which it was considered to replace the tail unit with the one of the ANT-40IS 2, however, it was never completed. Another considered change that was never made was to replace the radial engines with Mikulin AR-34RN ones. 

Anyway, the project for the APK-4 recoilless guns was cancelled due to the arrest of its creator, Leonid Kurchevsky, so the ANT-46 project was left on hold. It was considered to replace them with two 20 mm ShVAK cannons in each wing or with a gun pack containing five 12,7 mm ShVAK machine guns placed in the bomb bay, like the British Bristol Blenheim Mk.IF. However, interest was lost, the ANT-46 was never presented to state trials and in 1937 Tupolev was also arrested, so his initials were banned from aircraft denominations and the planes were officially called TsAGI-40 and TsAGI-46.

Once in production, the SB 2M-100 (the denomination for the first production variants, powered by two Klimov M-100 radial engines) saw combat in the Spanish Civil War, from where some feedback was collected to improve the type's defensive armament. These experiments included the installation of an MV-3 turret or a new enlarged glazed cockpit in order to improve lateral visibility. 

Those experimental variants were completed during the course of 1936 and 1937 and, while most of them were unsuccessful, some defensive arrangements were carried over for later variants.

Sources:

1st https://en.wikipedia.org/wiki/Tupolev_SB

2nd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/prototypes/ant-40-46.htm

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/prototypes/defensive.htm

4th Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

Tupolev SB in Spain. Part Two.

 

When the German Messerschmitt Bf.109B fighter made its appearance over Spain, with its experienced pilots, the losses of the SBs started to pile up. On 7th February 1938 four bombers were shot down, making it the worst loss rate in a single date, up to that date. By June 1938 only a handful of aircraft were serviceable, however, in July, thirty more SBs were delivered via France and were assembled at Figueres, Catalonia. This last delivery increased the total number of Tupolev SBs in Spain up to 93. 

During the conflict, one SB was captured by the Nationalist and received Aviación Nacional's (Nationalist Air Force) codes, was painted with Italian colours and camouflage pattern. It was shown at Tablada airfield (Seville) in October 1937.

One distinctive feature of the SBs assembled in Spain during the late-war period was the introduction of a fairing in front of the rear gunner's compartment. 

The code assigned by the Fuerza Aérea Republicana Española (FARE - Spanish Republican Air Force) to the SB was BK (which stands for Bombardero Katiuska - Katiuska Bomber) followed by a three-digit number, painted in black. Additionally, after a reform in FARE, some SBs received a two-digit number code painted in the tailfin.

The aerial superiority of the Nationalists, coupled with the inexperience of the Republican Katiuska's crews, quickly dropped the available number of SBs in the FARE. When the Spanish Civil War ended on 1st April 1939, a total of 73 SBs were lost, 40 of them to Nationalists actions. 

Shortly after the war, the reformed Spanish Ejército del Aire (Air Army - Spanish Air Force) created an unit with the captured and surrendered Katiuskas. This unit was called 13º Regimiento de Bombardeo (13th Bomber Regiment), based at Los Llanos airfield (Albacete - New Castile) and was composed of 19 Tupolev SBs. Some of these machines were re-engined with the Hispano-Suiza 12Ybrs engine, although the covering cowl was maintained, so, externally, there was no difference. This was done to ease maintenance, as they were still subject to spare shortages up to the point that, in April 1943, only three SBs were available. This forced Francoist authorities to ground the SBs and purchase some Junkers Ju.88A bombers from Germany which arrived in December 1943. The remaining Katiuskas were employed for occasional training flights until 1948, when they were scrapped.

Sources:

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/spanish/spanishrepublican.htm

4th http://elhangardetj.blogspot.com/2008/10/tablada.html (translated)

Tupolev SB in Spain. Part one.

 

In the early days of the Spanish Civil War, the Soviet freighter ship Komsomol shipped the first 31 Tupolev SB bombers from Odessa to the port of Cartagena, Murcia, south-eastern Spain. The Spanish Republican Government did pay  $110.000 US dollars per aircraft. Those SBs were part of one of the first production batches completed at GAZ-22 factory. They were unloaded on 15th October 1936 and assembles at Los Alcázares airfield, in the region of Murcia. 
The bombers were assigned to Grupo 12 (Group 12), which also operated the Polikarpov I-15 and I-16 fighters. Flying personnel, most of them, were Soviet, however, some Spanish and other international volunteers worked with the Grupo from its origin. Since the beginning of the conflict the SB was nicknamed as Katiuska by the Spaniards, after a popular character of a Spanish operetta, back at the time.

On 28th October 1936 the SBs flew their first combat mission when four Katiuskas belonging to 1ª Escuadrilla / Grupo 12 (1st Squadron / Group 12), under the command of the Swiss Ernst Schacht raided the Tablada airfield at Seville. After the attack, the SBs flew away at very high speeds, so Nationalists fighters couldn't intercept them, causing consternation among the Nationalists.

On 1st November 1936, three Katiuskas attacked the Gamonal airfield, in the city of Burgos, destroying six Fiat Cr.32 Italian fighters on the ground. The next day, two Cr.32 shot down one SB 2M-100 over Talavera, in new Castile. This loss showed its main flaw: the lack of both crew armour and self-sealing fuel tanks. 

On 6th November 1936 the SBs raided the airfield of Ávila, old Castile, destroying two Heinkel He.51 fighters of the German Condor Legion. These kind of raids, where a small group of Katiuskas targeted Nationalists airfields were very common in the months of November and December 1936. The first Spanish Nationalist pilot to claim a downed SB 2M-100 was Bermúdez de Castro. On 7th December he shot down a Soviet bomber over Castilblanco, Extremadura. By the end of the year 1936, Grupo 12 had lost a total of six out of 31 Katiuskas to various reasons.

In January 1937 the 1ª and 2ª Escuadrillas (1st and 2nd Squadrons) of Grupo 12, flew missions from Marbella, Andalusia, to try to stop the Nationalist advance on Málaga. On 20th January, some Nationalists strongpoints in Ceuta (Spanish Morocco) were bombed. During early March, the Katiuskas took part in the Battle of Guadalajara (old Castile) by bombing positions of the Italian Expeditionary Force. On 29th May 1937 two Katiuskas attacked the German Deutschland Panzerschiffe (Armoured Cruiser), off the coast of Ibiza, damaging moderately the cruiser in the attack.

The cargo freight SS Aldecoa arrived at the port of Cartagena on 24th June 1937 with 21 more Katiuskas, these were complemented with 10 additional ones shipped by the freighter SS Artea Mendi the next 1st July. This second batch was composed of the more powerful and improved SB 2M-100A model. The 31 new Katiuskas were assembled at San Javier, Murcia and Líria, in Valencia. They were assigned both to Grupo 12 and the newly formed Grupo 24. This new group flew its first combat mission on 3rd July when its two squadrons raided Talavera, Salamanca and Ávila. 

Both Grupos saw action during the Republican Offensive in Brunete (west of Madrid) on 6th July 1937. On 8th July a Katiuska was shot down by a Messerschmitt Bf.109B of the Condor Legion. Four days later, a Katiuska managed to shot down a Bf.109B that was attacking the formation of bombers.

In the Fall of 1937 Soviet crews were withdrawn and replaced by Spanish personnel, leading to the dissolution of Grupo 12 and assigning every Katiuska to Grupo 24. 

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/spanish/spanishrepublican.htm

Tupolev SB in Finnish service. Part one.

 

During the Winter War, which comprised from 30th November 1939 to 13th March 1940, the Finnish captured eight salvageable SB 2M-100A. Those were repaired and assigned to Ilmavoimat (Finnish Air Force), after the conflict, so they didn't see action with Ilmavoimat in the Winter War. However, eventually only one SB 2M-100A was in good enough conditions to be assigned to active service.

It was during that conflict that the Finnish managed to capture seven SB 2M-103, when many were forced to land in Finland.

The first SB 2M-103, registered as VP-10 by the Ilmavoimat, was overhauled at Valtion lentokonetehdas (State Aircraft Factory) at Tampere, Finland. On 13th August 1940 it was assigned to the Ilmavoimat and, on 15th October it was assigned to Lentolaivue 6 (LeLv - Flying Squadron) at Nummela. LeLv 6 was directly subordinated to Finnish Navy's Headquarters.

The Ilmavoimat re-registered the remaining SBs (among them the only SB 2M-100A which could be put into service) from VP-2 to VP-8. VP-10 was re-registered VP-1 in June 1941. During Continuation War, ranging from 25th June 1941 to 19th September 1944, LeLv 6 suffered its first casualty on 2nd August 1941 when VP-3 crash-landed at Nummela. The Finns changed the code for the remaining SBs in September 1941 but they didn't change the numerical suffix of each airplane. It was during this period that the SBs were repainted with yellow identification bands to identify them as Axis aircraft operating on the Eastern Front.

During the summer of 1941, the Germans captured several SBs in the context of Operation Barbarossa. Finland bought 16 SB 2M-103 from German war booty depots. On 5th November 1941 the six units arrived on Finland and were assigned codes SB-9 to SB-14. The following five were delivered in April 1942 and received codes SB-15 to SB-19. The last five ones reached Finland in August that same year. All those SB 2M-103 were refurbished at Valtion lentokonetehdas and some of them were equipped with additional carburetor intakes on the side of the engine cowling.

That made a total of 24 Tupolev SBs (23 SB 2-M103 and one SB 2M-100A) serving with the Ilmavoimat.

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/finnish/finnish-number.htm

Tupolev SB in service with China

 

On 7th July 1937 Japan invaded China sparkling the Second Sino-Japanese War. The Chinese Air Force (CAF) had, at that time just 284 aircraft and was commanded by General Moa Pang-chu who had learned to fly in the USSR. 

On 21st August both China and the USSR signed a non aggression pact, by virtue of which a secret clause was included to send military aid to China. This clause stressed on rebuilding the virtually destroyed Chinese Air Force. The Chinese negotiated a major loan with the USSR to provide China with war materials in exchange for cheap raw resources over the next five years.

During the course of October 1937,  four hundred fifty Soviet pilots and technicians were gathered at Alma Ata (Kazakh SSSR - nowadays Kazakhstan) from where they departed with a first batch of 185 aircraft (115 fighters, 62 bombers and 8 advanced trainers). These aircraft were transported by rail from Alma Ata to Lanzhou (province of Gansu) , where the Chinese railroad ended, following the trace of the old Silk Road. 

Chinese SB 2M-100-As (with old style cowlings) were all built at the GAZ factory No. 125 Imeni Stalina located at Irkutsk, in Siberia. Soviet pilots collected the first batch of bombers from the factory and ferried them from Irkutsk to Suzhou (in Gansu too) via Ulan Bator, Mongolia. Due to a sandstorm, the aircraft had to be grounded for a short time, before resuming the flight from Suzhou to Lanzhou. Many Soviet advisors began to train Chinese crews assigned to the 2nd Group of the CAF, on the SB 2M-100A. The first combat mission was led by Cpt. I.N. Kozlov on 2nd December 1937, when nine SBs attacked Japanese shipping in the East China Sea off the coast of Shanghai. 

A second batch of 31 SB 2M-100A was led by Cpt. Fiodor P. Polynin. These machines were ferried from Irkutsk to Hankou with stopovers at Ürümqi (Xinjiang), Hami (Xinjiang) and Lanzhou. The bombers were manned by Soviet crews until the Chinese were able to master the aircraft. A total of 150 sorties were flown by Soviet volunteers against Japanese airfields, riverine traffic and communications centers during the months of January and February 1938. One such mission took place on 25th January 1938 when 13 SB 2M-100A attacked the Japanese airfield at Nanjing (Jiangsu). 

On 23rd February Cpt. Polynin led a force composed of 28 SB 2M-100As to attack the airfield of Hsinchu, at north-western Formosa (Taiwan). The bombers were armed with ten bombs each and flew most of the distance from Lanzhou to Formosa across it straight at 5.500 m (18.045 ft) of altitude, causing headaches to crew members due to the lack of oxygen. In spite of this problem, the SBs approached Hsinchu from the north achieving total surprise when they dropped their bombs. Japanese anti-air fire proved ineffective and no Japanese fighters were put in the air to intercept the bombers. The SBs arrived back at Lanzhou without any incident after a seven-hour mission. Madame Chiang kai-shek, wife of the Chinese leader, rewarded the Soviet airmen with a banquet and decorations.

All those previously mentioned missions were flown without fighter escort, as the SB 2M-100A was the fastest bomber present on both sides of the Second Sino-Japanese War. These bombers suffered relatively low losses during combat and the biggest threat to them were Japanese raids on SB airfields.

A third Soviet bomber group (the exact number of flown aircraft is unknown) led by Georgy I. Tkhor left GAZ 125 at Irkutsk in late April 1938 and ferried to Lanzhou, this time via Ulan Bator and Dalanzadgad (Mongolia). This group took also part in many missions against the Japanese between the months of June and October 1938.

In late 1939 several SB 2M-103 were also supplied to the CAF. It was at this time when Soviet volunteer airmen began to leave China, as the Soviets became disillusioned and frustrated in spite of the fact that Soviet aid help to strength Chinese resistance against the Japanese. The Soviet aircraft were often misused and crashed when manned by Chinese crews as they lacked experience and therefore didn't follow (or didn't understand) Soviet instructions. The Chinese put the SBs in reserve, instead of flying them into combat.

On 27th December 1939 three SB M-103 of the last Soviet volunteer unit at Hengyang (province of Hunan) flew southwest to support Chinese ground troops at the Battle of Kunlun Pass. They were escorted by the last Gloster Gladiator fighters of 28th Squadron. After the Soviet withdrawal the remaining SB 2M-103s were assigned to the 1st and 2nd Groups of the CAF.

In 1940 a single Tupolev SB constituted the only offensive aircraft the Collaborationist Chinese Army Air Force (CCAAF - AKA Peacebuilding National Army) had. It was joined in September by another SB, piloted by Cpt. Zhang Diqin and manned by Lts. Tang Houlian and Liang Wenhua who defected to Nanjing, and were given substantial reward by the Japanese.

Chinese-manned SBs suffered heavy losses against experimented Japanese pilots. The USSR supplied 100 SB 2M-03 (including some SB 2M-105 -which was one of the last production variant-) in early 1941. These replaced some of the aircraft lost the previous years to accidents and combat. China became the largest foreign user of the SB with a total of 392 aircraft delivered straight from Soviet production lines. On 13th April 1941 Stalin and Japanese foreign minister Yosuke Matsuoka signed a neutrality pact. This resulted in a swift halt in the deliverance of Soviet war material to China, but the SBs were allowed to remain in CAF service. A formation of three SB 2M-103s made three attacks on Japanese troops crossing Dongting Lake (Hunan) and raided Yichang (province of Hubei) in September 1941. 

Chinese SB 2M-103 served well into 1943 and, in some missions, they were escorted by the Curtiss P-40 of the American Volunteer Group, the famous Flying Tigers.

Apparently some few SB survived World War 2 and took part, albeit in limited number and usage, in the last stage of the Chinese Civil War (1945-1949). 

Sources:

Sources:

1st Signal Squadron - Aircraft In action 194 - Tupolev SB in Action

2nd https://en.wikipedia.org/wiki/Tupolev_SB

3rd https://massimotessitori.altervista.org/sovietwarplanes/pages/sb/tapani/chinese/chinese.htm