The BT-5 went into production at the end of 1932 and remainded there until 1934 when it was superseeded by the BT-7 Model 1935
With 1884 samples produced it became a standard model and remained in service until 1941. Some BTs were also provided with fascines.
While many historians have derided the BT and T-26 as obsolete junk, in fact they were certainly superior to their most numerous German counterparts, the Pzkpfw I and Pzkpfw II in most respects, and their guns were certainly effective even against the Pzkpfw III.
Their main problem was the relative inexperience of their crews, the appaling deficiencies in the officer cadres in the wake of the purges, and the debilitating lack of spare parts.
Soviet tank output in the inter-war period exceeded that of any other nation, and in fact there were nearly as many BTs manufactured oetween 1931 and 1941 as there were tanks manufactured in the whole world from 1920-1940.
The problem was that the Soviets were fascinated with raw production numbers and ignored the crucial requirement for spare parts.
The massive losses of Soviet tanks in the summer of 1941 was due primarily to mechanical breakdown and not enemy action.
Sources : Milsom, »Russian BT series«, AFV Weapons #37, and Zaloga/Grandsen, »Soviet Fast Tanks«, Military Modelling Jan.1982