Deep operation
3. Operational
Operational is the bridge between tactics and strategy.
According to Colonel McPadden (US Army), the most precious legacy of Tukhachevsky is his concepts about all operations theory including the "operational art". Tukhachevsky is the first who used 'operational' as a systematic concept. According to McPadden, the main skill of a military commander is dependent on Tukhachevsky's theory, which is the ability to integrate tactics and strategy. This involves the capability of a commander on "the use of military forces to achieve strategic goals through the design, organization, integration and conduct of theater strategies, campaigns, major operations and battles."

Isserson; the factor of depth: Georgii Samoilovich Isserson (1898–1976) was a prolific writer on military tactics and operations. Among his most important works on operational art were The Evolution of Operational Art (1932 and 1937) and Fundamentals of the Deep Operation (1933). The latter work remains classified to this day.
Isserson concentrated on depth and the role it played in operations and strategy. According to his view, strategy had moved on from Napoleonic times and the strategy of a single point (the decisive battle) and the Moltke era of linear strategy. The continuous front that developed in the First World War would not allow the flanking moves of the pre-1914 period. Isserson argued that the front had become devoid of open flanks and military art faced a challenge to develop new methods to break through a deeply echeloned defence. To this end he wrote that "we are at the dawn of a new epoch in military art, and must move from a linear strategy to a deep strategy."
Isserson calculated that the Red Army's attack echelon must be 100 to 120 km deep. He estimated that enemy tactical defences, in about two lines, would be shallow in the first and stretch back 56 km. The second line would be formed behind and have 12–15 km of depth. Beyond that lay the operational depth, which would be larger and more densely-occupied than the first by embracing the railheads and supply stations to a depth of 50–60 km. There, the main enemy forces were concentrated. The third zone, beyond the operational depth was known as the strategic depth and served as the vital link between the country's manpower reservoirs and industrial power-supply sites and the area of military operations. In this zone lay the headquarters of the strategic forces, which included the army group level.
Isserson much like Varfolomeev divided his shock armies, one for the task of breaking the enemy forward (or frontline defences) and the other to exploit the breakthrough and occupy the operational zone, while destroying enemy reserve concentrations as they attempted to counter the assault. The exploitation phase would be carried out by combined arms teams of mechanized airborne infantry and motorised forces.
The breadth of the attack zone was an important factor in Soviet calculations. Isserson asserted an attack over a frontage of 70–80 km would be best. Three or four rifle corps would make a breakthrough along a front of 30 km. The breakthrough zone (only under favourable conditions) might be expanded to 48–50 km with another rifle corps. Under these conditions, a rifle corps would attack along a 10–12 km front, with each division in the corps' first echelon allocated a 6 kilometre frontage. A fifth supporting rifle corps would make diversionary attacks along the flanks of the main thrust to tie down counterresponses, confuse the enemy as to the area of the main thrust and delay its reserves from arriving.

Tactical deep battle: Once the strategic objectives had been determined and operational preparation completed the Red Army would be tasked with assaulting the tactical zones of the enemy front in order to break through into its rear, allowing operationally mobile forces to invade the undefended enemy-held area to the rear.
The Soviet rifle corps was essential to the tactical method. As the largest tactical unit it formed the central component of the tactical deep battle. The rifle corps usually formed part of a larger operational effort and would be reinforced with tanks, artillery and other weapons. Several corps would take part in the attack, some with defensive missions and others with offensive assignments. They were known as holding and shock groups, respectively.
The order of battle was to encompass three echelons. The first echelon, acting as the first layer of forces, would come into immediate contact with opposing forces to break the tactical zones. The follow on echelons would support the breakthrough and the reserve would exploit it operationally. The holding group would be positioned on either flank of the combat zone to tie down enemy reinforcements via means of diversion attacks or blocking defence.
Nevertheless, despite the diversion being a primary mission, the limited forces conducting holding actions would be assigned geographical objectives. Once the main thrust had defeated the enemy's main defence, the tactical holding forces were to merge with the main body of forces conducting the operations.
In defence, the same principles would apply. The holding group would be positioned forward of the main defensive lines. The job of the holding echelons in that event was to weaken or halt the main enemy forces. If that was achieved, the enemy would be weakened sufficiently to be caught and impaled on the main defence lines. If that failed, and the enemy succeeded in sweeping aside the holding forces and breaching several of the main defence lines, mobile operational reserves, including tanks and assault aviation, would be committed. These forces would be allocated to holding and shock groups alike and were often positioned behind the main defences to engage the battle worn enemy thrust.
The forces used to carry out the tactical assignments varied from 1933 to 1943. The number of shock armies, rifle corps, and divisions (mechanized and infantry) given to a strategic front constantly changed. By 1943, the year that the Red Army began to practice deep battle properly, the order of battle for each tactical unit under the command of a front were:
Rifle army

3 rifle corps
7–12 rifle divisions
4 artillery regiments
One field artillery regiment
One anti-tank gun regiment
anti-aircraft artillery regiment
One mortar regiment
One signal regiment
One communication battalion
One telegraph company
One aviation communication troop
Stavka operational forces

1–2 artillery divisions
3 artillery regiments
3 tank destroyer regiments
3–4 tank or self-propelled gun brigades
10 separate tank or self-propelled gun regiments
2 anti-aircraft divisions
1–2 mechanized corps
These forces numbered some 80,000–130,000 men, 1,500–2,000 guns and mortars, 48-497 rocket launchers, and 30-226 self-propelled guns.
Rifle corps

3 Rifle divisions
One artillery regiment
One signals battalion
One sapper battalion
Rifle division

3 Rifle regiments
One artillery regiment
One anti-tank battalion
One sapper battalion
One signal company
One reconnaissance company
The division numbered some 9,380 men (10,670 in a guards rifle division), 44 field guns, 160 mortars and 48 anti-tank guns.

Deep operation: Soviet analysts recognised that it was not enough to break through the enemy tactical zone. Although that was the crucial first step, tactical deep battle offered no solution about how a force could sustain an advance beyond it and into the operational and strategic depths of an enemy front. The success of tactical action counted for little in an operational defensive zone that extended dozens of kilometres and in which the enemy held large reserves. Such enemy concentrations could prevent the exploitation of a tactical breakthrough and threaten the operational advance.

That was demonstrated during the First World War, when initial breakthroughs were rendered useless by the exhaustion during the tactical effort, limited mobility, and a slow-paced advance and enemy reinforcements. The attacker was further unable to influence the fighting beyond the immediate battlefield because of the limited range, speed and reliability in the existing weapons. The attacker was often unable to exploit tactical success in even the most favourable circumstances, as his infantry could not push into the breach rapidly enough. Enemy reinforcements could then seal off the break in their lines.
By the early 1930s, however, new weapons had come into circulation. Improvements in the speed and range of offensive weaponry matched those of its defensive counterparts. New tanks, aircraft and motorised vehicles were entering service in large numbers to form divisions and corps of air fleets, motorised and mechanized divisions. Those trends prompted the Red Army strategists to attempt to solve the problem of maintaining operational tempo with new technology.
The concept was termed "deep operations" (glubokaya operatsiya), which emerged in 1936 and was  placed within the context of deep battle in the 1936 Field Regulations. The deep operation was geared toward operations at the Army and or Front level and was larger, in terms of the forces engaged, than deep battle's tactical component, which used units not larger than corps size.
The forces used in the operational phase were much larger. The Red Army proposed to use the efforts of air forces, airborne forces and ground forces to launch a "simultaneous blow throughout the entire depth of the enemy's operational defense" to delay its strongest forces positioned in the area of operations by defeating them in detail; to surround and destroy those units at the front (the tactical zone, by occupying the operational depth to its rear); and to continue the offensive into the defender's operational and strategic depth.