https://en.wikipedia.org/wiki/Deep_operation
The impact of the purges
(...) By 1937, the Soviet Union had the largest mechanized army in the world and a sophisticated operational system to operate it.
However, the death of Triandafillov in an airplane crash and the '
Great Purges' of 1937 to 1939 removed many of the leading officers of the Red Army, including Svechin, Varfolomeev and Tukhachevsky.
[32] The purge of the Soviet military liquidated the generation of officers who had given the Red Army the deep battle strategy, operations and tactics and who also had rebuilt the Soviet armed forces. Along with these personalities, their ideas were also dispensed with.
[33] Some 35,000 personnel, about 50 percent of the officer corps, three out of five marshals; 13 out of 15 army group commanders; 57 out of 85 corps commanders; 110 out of 195 division commanders; 220 out of 406 brigade commanders were executed, imprisoned or "discharged". Stalin thus destroyed the cream of the personnel with operational and tactical competence in the Red Army.
[34] Other sources state that 60 out of 67 corps commanders, 221 out of 397 brigade commanders, 79 percent of regimental commanders, 88 percent of regimental chiefs of staff, and 87 percent of all battalion commanders were excised from the army by various means.
[35]
Soviet sources admitted in 1988:
In 1937–1938 ... all commanders of the armed forces, members of the military councils, and chiefs of the political departments of the military districts, the majority of the chiefs of the central administrations of the People's Commissariat of Defense, all corps commanders, almost all division and brigade commanders, about one-third of the regimental commissars, many teachers of higher or middle military and military-political schools were judged and destroyed.
[36]
The deep operation concept was thrown out of Soviet military strategy as it was associated with the denounced figures that created it.
Deep operations during World War II
The abandonment of deep operations had a huge impact on Soviet military capability. Fully engaging in the Second World War (after Winter War) the
German invasion of the Soviet Union in June 1941, the Soviets struggled to relearn it. The surprise German invasion (
Operation Barbarossa) subjected the Red Army to six months of disasters. The Red Army was shattered during the first two months. Thereafter it faced the task of surviving, then reviving and maturing into an instrument that could compete with the
Wehrmacht and achieve victory.
Soviet military analysts and historians divide the war into three periods. The Red Army was primarily on the strategic defensive during the first period of war (22 June 1941 – 19 November 1942). By late 1942 the Soviets had recovered sufficiently to put their concept into practice. The second period of war (19 November 1942 – 31 December 1943), which commenced with the Soviet strategic
counteroffensive at Stalingrad, was a transitional period marked by alternating attempts by both sides to secure strategic advantage. After that deep battle was used to devastating effect, allowing the Red Army to destroy hundreds of
Axis divisions. After the
Battle of Kursk the Soviets had firmly secured the strategic initiative and advanced beyond the
Dnepr River. The Red Army maintained the strategic initiative during the third and final period of war (1944–1945) and ultimately played a central role in the Allied victory in Europe.
[37]