The Tupolev design was advanced but lacked refinement, much to the dismay of crews, maintenance personnel, and Stalin, who pointed out that "there are no trivialities in aviation".

Many versions saw extensive action in Spain, the Republic of China, Mongolia, Finland and at the beginning of World War II against Germany in 1941.

[clarification needed] By June 1941, 94 percent of bombers in the Red Army air force (VVS RKKA) were SBs.

It was however plagued by teething problems, leading unhappy test personnel to cover the ANT-402 with placards listing the aircraft's defects prior to a visit by Sergo Ordzhonikidze, the Commissar for Heavy Industry.

[6] Despite the fact that the assembly lines were plagued with a constant string of modifications, some 400 SBs were delivered by the end of 1936—a number of these being diverted to Spain—and 24 VVS squadrons were in the process of working up with the new bomber.

[8] In 1937, negotiations were concluded between the Soviet and Czechoslovak governments, for the supply of SB bombers and a licence for local production, in exchange for the right to produce the Škoda 75 mm Model 1936 mountain gun.

As problems were encountered in converting pilots to fly the SB, a trainer version, the USB was built in September 1937, with a modified nose with an open cockpit for an instructor and dual controls.

[11][12] Problems were also encountered with the armament, the nose guns having limited traverse and so being little use against head-on attacks and later aircraft were modified with a better field of fire.

Alexeev set an official altitude record of 12,246 m (40,177 ft) with load of 1,000 kg (2,200 lb) in an M-103 powered SB.

[17][18] 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.

Because of its broad, high aspect ratio wing, that gave it a good altitude performance – Soviet crews nicknamed the SB the "Pterodactyl".

[28] 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.

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.

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.

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.

[37] 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.

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.

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 time of the Continuation War against the Soviet Union, five SBs had been repaired (with a further three added later), being used to equip Lentolaivue 6, flying maritime patrol and attack missions.

In the late 1970s, however, Vozdushni Transport (A Soviet aviation newspaper) sent an expedition led by Evgeny Konoplev to survey an ANT-40 that was forced to land during a snow storm near the Yuzhne Muiski mountain range in the Baikal region.

Konoplev considered what they found encouraging, with the aircraft being in fairly decent condition, in turn leading a team of VVS pilots to recover the airplane.