Hiya, folks!

I've just finished a major write-up on /r/Askhistorians in this thread, concerning the importance of the mobilisation of Soviet reserves throughout 1941. Given it's never going to be spotted in that thread and I just spent twelve hours writing it, I'd love to share it here, since I'm a sucker for attention I thought it would be relevant. I'll leave it un-modified from the AH version, so it is geared specifically towards Moscow. Apologies if that causes any strange parsing!

Reinforcements raised for the Red Army - largely from the Soviet interior, the mobilisation of reserves and the transfer of troops from the far-east and other sectors of the Soviet Union, were absolutely critical in the defence of Moscow from October-December, 1941. This needs to be viewed in context, however. Moscow was far from unique in this regard - it was the almost unfathomable ability of the Soviet Union to constantly raise, equip and deploy reserve forces during the first six-months of conflict on the Eastern front that proved critical in the defence not just of Moscow, but of the entire 2,500km (by October, 1941) front line. I cannot stress enough the sheer scale of mobilisation undertaken by the Red Army during the period June-December 1941, which repeatedly allowed the USSR to re-establish contiguous defensive lines following encirclements and losses which would have devastated any other military on the planet. I'll break this down into several discussions - the mobilisation of Red Army reserve forces June-October, 1941, the strategic situation at the commencement of Operation Typhoon (the German assault on Moscow), and finally the progress of the battle and the role of Red Army strategic reserves in determining its outcome.

On Red Army reserves in 1941

At the onset of Operation Barbarossa on June 22, 1941, the Red Army stood at a strength of roughly 5.5 million men, of whom approximately 3.3 million were concentrated in the Western districts - that is, who were in any position to react to the Axis invasion.¹ This initial number alone is formidable, but belies the unfathomable strategic depth of the USSR at the point of the German invasion. The 1938 Universal Military Service Law ensured that the military infrastructure existed for the rapid mobilisation of a vast portion of the USSR's population, creating an effective manpower pool of some fourteen million reservists as well as the training schools and marshalling capabilities to call on them in short order. With the full mobilisation of the Red Army beginning June 22, 1941 following the Axis invasion, absolutely phenomenal efforts began for the organising, equipping and deployment of new forces. By the time the first phase of mobilisation was complete on July 1, 1941, the Red Army's nominal strength had increased from 5.5 million troops to 9.5 million troops. Naturally, the organisation, equipment and deployment of such a colossal force proved an extremely chaotic process, and the vast majority of the levied forces were of low quality and still in the Soviet interior, far from the front-line opposition to the Axis advance. Nonetheless, this was only the beginning of the Soviet mobilisation process. To quote Stahel:

"In July the Red Army added thirteen new field armies to its order of battle and fourteen more in August. In September there was one new army, in October four and in November and December eight, making a total of forty new Soviet armies in just six months."²

Herein lies a critical difference between the advancing Axis forces and the defending Soviets during Operation Barbarossa. As the offensive pressed deeper into the USSR, the offensive strength, organisation and capabilities of the Axis forces were constantly eroded by casualties, mechanical failure, and critical over-stretched logistics. In comparison, despite the encirclement and destruction of Soviet armies totaling more than three million men, the loss of more than 10,000 tanks and guns, and thousands of aircraft, the Red Army was larger in October 1941 than it was in June. Clauswitz, in his famous work On War describes this action as the 'culminating point' of an attack - where the strength of the attacker is constantly depleted as an offensive wears on without a decisive outcome, while the strength of the defender continually increases. When the strength of the defender exceeds that of the attacker, the attack fails, and will often be followed by a 'hammer blow' of a counter-attack. The culminating point - though not the deciding point - of Operation Barbarossa was the battle of Moscow.

On Estimates, Battle-Plans and Reality

So, the end result of this massive mobilisation process was that the central strategic tenet of the Axis offensive - the encirclement and destruction of the Red Army before the strategically significant Dvina-Dnieper line, was impossible. The Axis strategy hinged on the idea that the Red Army could be effectively destroyed in a series of massive encirclements in Poland and western Russia, and would thus be unable to form a contiguous (constant, connected) front further in the Soviet interior. Such a plan relied on the idea that subsequent reinforcement from newly raised or redeployed Soviet forces would not be capable of forming a major strategic reserve, or of forming a solid defensive line further East. In the event that such a line was formed, German planners assumed that the strategic double-pincer encirclements deployed early in Barbarossa would be repeated against further formations, to similarly cut-off, encircle and destroy them.

The reality of the situation was that German intelligence woefully under-estimated the massive number of reserve forces that would be raised from the Soviet interior. As I stated above, nearly the entire Red Army's strength again had been raised in the Soviet Interior within ten days of the commencement of Operation Barbarossa. The most pessimistic German planners made allowances for ~30 new Soviet divisions to be raised within the first three months of conflict, rising to ~140 divisions within six months of the commencement of operations.³ Even under these projected circumstances, the German invasion faced massive logistical and military problems in wargames. With effectively no reserves of their own to draw on, the German invasion would lose steam as its roughly 3,000,000 men were dispersed across the widening funnel of Eastern Europe, with the front expanding from ~1,500km to ~2,500km. Units suffered heavy losses from combat and were rapidly behind schedule even in wargames, which proved critically optimistic in their assumptions of Soviet force estimates and German logistical capabilities.⁴

In any event, the German projections that the Soviets would raise roughly 2,000,000 reserves in six months were proven catastrophically optimistic - the Red Army had raised 4,000,000 reserves in ten days,⁵ and would raise an additional three million by the end of the year.

On the failure of Barbarossa

Despite the massive encirclements and colossal losses of men and materiel suffered by the Soviets,⁶ the OKH (Oberkommando des Heeres, the German Army High Command) began to realise the extent of its predicament as soon as early August - the Soviets were forming new armies faster than they could be destroyed. There were too few encirclements, too many Soviet forces falling back successfully, and too many delays. Additionally, casualties suffered by Axis forces mounted rapidly, and despite the initial success of the Blitzkrieg and the encirclement of vast Soviet forces, the offensive capabilities of the Wehrmacht were being eroded at an alarming rate. As early as July 11, Field Marshal Wilhelm Ritter von Leeb, commander of the German Army Group North, recorded in his diary

"heavy losses... If further attacks are to be conducted at this pace we will soon reach a state of exhaustion."⁷

The invasion soon lagged badly behind schedule, and on August 11, 1941, the OKH Chief of Staff, General Franz Halder, observed

"At the outset of the war, we reckoned on about 200 enemy divisions. Now we have already counted 360... if we smash a dozen of them, the Russians simply put up another dozen."⁸

The result of the constant flow of new Soviet formations to the front was that, as the Axis pushed deeper into the Soviet interior, Axis offensive strength was rapidly sapped and the advance impeded by heavy casualties, eroded capabilities and overstretched logistics. Despite the destruction of a great deal of the Red Army between June and September 1941, the mass-mobilisation of Soviet reserves ensured that fresh forces were available to re-establish the line each time the Axis broke and encircled a portion of it. With each offensive, each defensive line and each encirclement, the critical German Panzer divisions became weaker and more overstretched, the front widened, and the logistics situations worsened. By late July - early August, the Axis offensive ground to a halt due to casualties and supply problems. A major portion of the central thrust was redirected towards Ukraine when the offensive restarted in late August, which resulted in a successful encirclement at Kiev but further weakened the drive on Moscow. Even prior to the beginning of Operation Typhoon on October 1, 1941, the invasion was failing. The Soviet line had been re-established, reinforcements had slowed the offensives and greatly sapped their strength, and the lightning advance had become a dangerous meatgrinder, where Soviet forces were constantly reinforcing while those of the Axis were constantly depleting. Again borrowing from Stahel,

"Indeed the first three months of Operation Barbarossa proved the costliest quarter on the eastern front unil the first quarter of 1943, when the Germans suffered disaster at Stalingrad. In these opening months of the war the Ostheer suffered an estimated 185,198 dead, which comes to 14,420 men a week or the equivalent of having on division eliminated to the last man every week, and this does not count German wounded."⁹

In comparison, despite the massive losses suffered by the Red Army throughout the first three months of the campaign, and the devastating losses of the Kiev encirclement, August-September 1941, the Red Army was significantly larger at the commencement of Typhoon than it was at the commencement of Barbarossa. Unfortunately, I don't have the time at the moment to give an in-depth discussion of the entirety of Operation Barbarossa from go to woe - as I'm sure you'll appreciate it deserves a post all of its own and you asked specifically about Moscow. Nonetheless, as you can see from the above discussion, the mobilisation of more than 400 Soviet divisions in 40 field armies within six months had already proven critical to the delaying and ultimate failure of Barbarossa by the commencement of Operation Typhoon in October, 1941.

On Typhoon and the Battle of Moscow.

It is within the above context that we should discuss Soviet reinforcements during the Battle of Moscow. As a result of the incredibly costly but nonetheless successful delaying defence of the Red Army, Barbarossa was badly flagging. Stahel (who you've probably noticed I'm fond of!) makes the following observation:

"In his 1812 campaign Napoleon invaded Russia two days after the date chosen by Hitler (24 June) and entered Moscow on 15 September. In eighty-four days, with no motorization or railways, the French emperor had reached and taken Russia's largest city. On 26 September 1941 as the vast battle of Kiev came to an end, Hitler's campaign was on its ninety-seventh day and he was still 300 kilometres from Moscow."¹⁰

German Forces for Typhoon

The massive on-paper size of the German force assembled for Operation Typhoon belied the greatly weakened state of the Ostheer by the time the battle began on October 2. Field Marshal von Bock's Army Group Centre was assigned the drive on Moscow, with an assembled force of fourteen panzer, eight and a half motorized, one cavalry, forty seven infantry and five security divisions, most of which had been mauled by the previous three months' fighting.¹¹ While they totalled an impressive sum of 1,900,000 men,^12, they were exhausted, poorly supplied, and now represented the concentrated majority of the Ostheer's fighting strength - roughly 60% of all German armed forces at the time.¹³ Indeed, while the twelve panzer divisions Bock had controlled on June 22 totalled some 2,476 tanks, the fourteen he controlled on October 2 totalled just 1,530 tanks between them.¹⁴ The Luftwaffe, upon whose air support the Ostheer relied, was similarly beleaguered following four months of brutal warfare. Wolfram von Richthofen, commander of the Eight air corps - providing primary air support for Typhoon - noted with concern prior to the offensive that his corps had only 50% the total of functional aircraft for which preliminary planning had made allowance.¹⁵ Despite the massive consolidation of Luftwaffe assets in support of Typhoon, the offensive was to be supported by just 1,006 craft of of all models,¹⁶ whereas the far smaller Army Group Centre had been supported by 1,235 aircraft across a far smaller frontage at the beginning of Barbarossa.¹⁷

The frontage which Bock's depleted forces had to cover was 760km, compared with ~500 for the same concentration of forces (with more mechanised support) during Barbarossa. Bock's taskforce was a formidable army, but was nonetheless a shadow of the army that had invaded the USSR in June that year. To achieve this concentration of forces, the army groups to the north and south of Bock's Centre had been badly weakened, and reserves had been all-but exhausted. General Chales de Beaulieu observed in his memoirs that by late September:

"at the time what one referred to as a "division" was actually only half a division."¹⁸

The German Army had drawn together the greatest force it could muster for the invasion of Moscow, weakening its other fronts and exhausting all its remaining offensive strength - and it would prove insufficient.

Soviet Forces for Typhoon

Opposing Bock's reinforced Army Group Centre along the 760km frontage that would upon which Typhoon would be fought were some fifteen Soviet field armies. These armies were deployed in two echelons across three defensive lines west of Moscow.^A The first echelon, consisting of eleven armies and some 800,000 men, was deployed largely on the wastern-most of the three defensive lines, the Briansk Line, though auxiliary forces were also stationed along the Rezhev-Viazma line.¹⁹ The second echelon of four fresher field armies totalling some 450,000 men deployed along the Rezhev-Viazma and eastern-most Mozhaisk lines. The deployment of the vast majority of the forces defending Moscow well forward along the Briansk line was undertaken in response to intelligence estimates suggesting an offensive was all but imminent - it was also a critical mistake, greatly reducing the depth of the defence and all but inviting another encirclement calamity.^{20, B}

In support of these forces were some 7,600 guns, 1,000 tanks and 670 aircraft.²¹ Though the Soviets lacked the same quantity of tanks and aircraft available to Army Group Centre, the majority of the defenders' tanks were new T-34 and KV-1 model tanks, far superior to any model available to the Ostheer at the time.^C Additionally, the Soviet air arm was recovering rapidly from its massive losses during the initial stages of Barbarossa, and by Typhoon was in a far better supply situation than the Luftwaffe, operating off established airfields with good access to supplies and spare parts.²²

The Red Army forces barring the way to Moscow had been heavily mauled, reconstituted, re-designated and reinforced by the constant arrival and deployment of reserve forces. They were outnumbered by ~1.4:1 by Bock's Army Group Centre (far from a favourable ratio for a strategic offensive) and had three defensive lines of increasing strength with which to blunt the Axis advance. Were it not for their criminally poor deployment along the foremost of these lines, the Ostheer's advance might well have been blunted far further from the outskirts of Moscow than it ultimately would be.

Disaster at Briansk/Viazma

Army Group Centre opened Operation Typhoon in much the same way as previous offensives on the Eastern front - a massive double-pincer envelopment. Working in conjunction, the Third Panzer Group broke through Soviet defences north of the Briansk Line and outflanked the strongpoints of the Rezhev-Viazma Line, with elements anchoring the mainstay of the Soviet defenders' forces on the Briansk Line. Meanwhile the Fourth Panzer Group broke through south of the Briansk Line, mirroring the third. With the majority of the Red Army's forces forward-deployed, the speaheads met with comparatively little organised defence and linked up on October 11 at Viazma, having outflanked and cut off two of the three defensive lines before Moscow.²³ A massive portion of the Soviet force was unable to withdraw in the face of the onslaught, with as many as 750,000 men being cut off in the massive pocket that resulted from the encirclement.^24. Exactly how many troops would break out of this encirclement and successfully withdraw to the still-intact Mozhaisk Line is unclear, but the defeat was calamitous, its conditions largely precipitated by the terrible deployment of Soviet forces.

Despite the massive losses already incurred and the sudden and disastrous destruction of two defensive lines, Moscow was far from being Germany's-for-the-taking. A vast proportion of Army Group Center's forces - roughly 1/3 of its 75-and-a-half divisions - was tied up shrinking and destroying the trapped defenders of the Briansk and Rezhev-Viazma Lines. Furthermore, the arrival of the Rasputitsa, and its constant rain and mud, greatly hindered the operation of German forces, rapidly rendering roads into quagmires and making many of the Luftwaffe's airfields unuseable.^25,D The resulting delays bought time for the Soviets to reinforce the Mozhaisk Line, both with the remnants of the defending forces from Briansk and Rezhev-Viazma, and, critically, with huge numbers of reserve forces scraped up from all available sources.

The Mozhaisk Line, Reinforcements and the Defeat of Typhoon

By October 13, Ostheer forces were coming into contact with the Mozhaisk Line. Following the disasters at Briansk and Viazma, the remaining forces defending Moscow were critically weakened, with between 90,000²⁶ and 200,000²⁷ men manning the Mozhaisk Line as of October 10. This number would obviously be insufficient to resist the onslaught of the still-largely-cohesive Army Group Centre, and it is here that reserve forces would prove crucial to the defence of Moscow. Between the start and the end of October, four Soviet armies would be constituted effectively from scratch in the vicinity of Moscow, using remnants of the Briansk-Viazma lines, civilian levies raised from the city's population and multiple divisions transferred from less desperate sectors of the front and the Soviet interior. The forces raised, organised and deployed throughout October greatly strengthened the beleaguered defences of the Mozhaisk Line, in a defensive action far better managed than the debacles further West.^E

Despite the remarkable organisation and reinforcement of the forces defending Moscow, the Mozhaisk Line was slowly overrun throughout Mid-late October, 1941. Two of its anchors, Mozhaisk and Maloiaroslavets, fell on October 18, and the line was being outflanked both to the north and the south by October 24. To avoid facing another encirclement, Zhukov was forced to abandon the Mozhaisk Line on October 27, ordering a general withdrawal to hastily established defences along the Nara River, less than 40km from Moscow.²⁸ Although it fell, the Mozhaisk Line had served its purpose. Army Group Centre had been severely mauled, and OKH was forced to call a halt to offensive operations on October 31 to reorganise its battered forces and solve severe logistical problems caused by the Rasputitsa and its massive, vulnerable supply lines.

Between the abandonment of the Mozhaisk Line on October 27 and the resumption of OKH offensive operations on November 15, the Soviet defenders of Moscow received more than 200,000 reinforcements from freshly raised levies, reorganised remnants and, critically, from a several divisions transferred from the Far East.^29,F By comparison, German forces were receiving very few reinforcements, and suffering increasingly severely from the worsening Winter conditions and severe supply shortages. The renewed German offensive, concentrated in two pincers to the Northwest and Southwest of the city, was undertaken with greatly depleted, exhausted forces against a constantly strengthening enemy, now supported by increasingly elaborate earthworks and defensive emplacements.³⁰ Through fifteen days of desperate fighting, the Ostheer breached the Red Army's defences in several areas, but ultimately failed to force a breakthrough. By December 1, Army Group Centre was exhausted, crippled, and critically over-extended. The culminating point of Operation Typhoon had been reached.

Conclusion: The Hammer Blow, December 5, 1941 - January 7, 1942

As the Ostheer exhausted itself against the defences West of Moscow, the Red Army was preparing a counter-attack. Facilitated by the constant arrival of massive numbers of reserves throughout November, 1941, Zhukov had a force of eleven fresh armies totaling some 58 divisions at his disposal by early December.³¹ On December 5 this massive new reserve was deployed in a two-pronged offensive aimed at cutting off the over-extended 'pincers' to the northwest and southwest of Moscow.^G OKH had not anticipated that the Soviets would have any strategic reserve left whatsoever, let alone one large enough for a strategic counter-offensive, and were by-and-large caught completely off-guard by the ferocious counter-attack.³² With the Luftwaffe effectively grounded by the incredibly bitter winter conditions and the Ostheer's reserves completely spent, the damage dealt by the Red Army's counter-offensive was tremendous, resulting in massive German losses in men and materiel. While full-scale encirclements of the German Fourth Army and Third and Fourth Panzer Armies in the northwest pincer were just barely avoided, it was clear that the Red Army had survived the onslaughts of Barbarossa. By the time the offensive was called off on January 7, 1942, the Ostheer was badly mauled, the Red Army was intact, and the threat to Moscow had passed.

I'd like to close with a fantastic quote from Richard Overy's Why the Allies Won, which in my opinion sums up the incredible tenacity of the Soviet Union's war effort magnficiently:

"The key to the eventual victory of the Allied states lies here, in the remarkable revival of Soviet military and economic power to a point where the Red Army could first contain, then drive back the German invader: remarkable, because it followed the loss by December 1941 of 4 million men, 8,000 aircraft and 17,000 tanks, equivalent to almost the entire strength of the Soviet forces in June. Remarkable, because it followed the German capture of more than half the Soviet steel and coal output, and the entire Soviet 'breadbasket,' the fertile black earth regions of the Ukraine and the western steppe... So severe was the mauling that it is hard to imagine any modern state under these circumstances continuing to fight."³³

Thanks very much for reading. Hopefully this has been of interest/use. Under the watchful eye of all you nerds military history enthusiasts, I'm hopeful you'll point me in the right direction if I make any mistakes. Otherwise if you have any questions or feedback, it would be greatly appreciated!