Stalingrad for the Soviet Union was a complete tactical and morale turnaround for its soldiers and people. Before this point many soldiers and citizens had doubts as to whether they could compete or crush the Wehrmacht completely, aside from reassurances in propaganda or from political attaches like Commissars. Even with their doubts many soldier had no qualms about fighting and dying against an enemy that campaigned for their total destruction. Resistance was desperate and harsh and the focus put upon their actions was one of revenge and making the other die so that you don't have to - as emphasized by Poems (widely read and disseminated at the time) like Simonov's Kill Him

So kill that German so he

Will lie on the ground's backbone,

So the funeral wailing will be

In his house, not in your own.

He wanted it so It's his guilt

Let his house burn up, and his life.

Let his woman become a widow;

Don't let it be your wife.

Don't let your mother tire from tears;

Let the one who bore him bear the pain.

Don't let it be yours, but his

Family who will wait in vain.

So kill at least one of them

And as soon as you can. Still

Each one you chance to see!

Kill him! Kill him! Kill!

or even more poignant would be Ilya Ehrenberg's kill

If you kill one German, kill another -

there is nothing more amusing for us than a heap of German corpses

Do not count days; do not count miles

. Count only the number of Germans you have killed

. Kill the German - this is your old mother's prayer.

Kill ther German - this is what your children beseech you to do

. Kill the German - this is the cry of your Russian earth.

Do not waver. Do not let up. Kill.

The Soviet's were in a dire situation by the summer of 1942 and needed a large victory not only to prove that they could still prevail in the most adverse of conditions, but also a major turn around for the whole front - which, although close, was almost enacted with the major counter offensive around Moscow in the winter of 1941. Stalingrad was more than just a symbol with the leaders name on it, Stalingrad was also to the Germans and Russians - the Gateway to Asia, the border between two continents on the Volga. Below it in the Caucasus also lay the oilfields at Maykop (which the Soviets set ablaze), Grozny, and Baku on the Caspian Sea. Cutting the Volga at Stalingrad would also cripple supplies of fuel and industry North to other important sectors of the country as Stalingrad its self held many large industrial concerns like the Tractor Works, Barrikady, and Red October works. This was a model center for the socialist ideal put forth by the Government at the time with its wide boulevards, large industrial concerns, and sweeping parks for its residents to enjoy. All this was promptly shattered when most of the city was flattened in the concentrated air assault by Wolfram Freiherr von Richthofen's Luftflotte. The loss of this city would not be tolerated under any circumstance, and the prescience of Stalin's order number 227 - not one step backwards - was made evident by soldier's anecdote that "there is no land for us beyond the Volga".

The fanatical defense and the major turnaround for the beleaguered 62nd army in the city and the massive encirclement of Operation Uranus shocked many in the Wehrmacht into disbelief at the size and scale of an offensive pulled off by an army supposedly on its last legs - incapable of mounting a massive counter offensive. Soviet soldier's were ecstatic when the pincers of the attack met at Kalach and greeted each other with unrestrained exuberance - although there is a famous film of the incident, it is actually a re-enactment of the meeting of the two army groups. This sealed the fate of the 6th army trapped in the Kessel around the city and its outlying areas; even though Von Manstein would mount an attempt to relieve the trapped army - they had no orders and were under no circumstances to retreat or break out from their positions per Hitler's direct orders. They were trapped and would have to live through the next few terrible months on starvation rations boosted by intermittent Luftwaffe transports attempted to make up for the lack of supply lines in the Kessel (300 tons per day were needed to keep them alive, 500 to maintain operational ability, less than 100 typically made it through on a good day). The Germans were on their dire straights in the last few months of the battle, but the frustrating pace at which the Red Army was closing the ring around the 6th army was becoming irritating and worrisome for many participating in the final operations of the battle. It wasn't until the end of January in 1943 that the 6th army finally surrendered in the ruins of 'fortress Stalingrad' and the remaining 120,000 or so prisoners would be marched off to captivity, in which almost all would perish. Less than 7000 of those would ever return home, most of them junior or senior officers.

The Morale boost across the whole of the front is almost immeasurable - whole armies were exuberant to hear of the miracle that had transpired at the bloody battle. Soldier's now had the impression that it was now the time to exact a bloody vengeance upon the invading armies in the same light as they had done to them. All this was exacerbated by propaganda and poems outlined above - that according to authors like Anthony Beevor, may have contributed to the carnage and mass sexual violence that occurred when the Red Army entered German territory. It was now firmly the Red Army's turn to regain the initiative and push the German's out of Soviet land. This was a morale victory like nothing that had ever been seen during the course of the Eastern Front. Many of the battalions that had fought in the city or during the course of the counter attack were parceled out to different armies and fronts across the whole of the Eastern Theater in order to boost the morale and fighting capacity of them with hardened veterans and heroes of the Battle of Stalingrad.

I'm not exactly sure you could say it was Russia's "D-Day" as D-day has many different connotations for different countries involved. D-Day was the start of the Allied campaign for Western Europe, while Stalingrad was a turn around of the fighting on the Eastern Front - not so much to beginning or ending of anything, more accurately a climax of events in a turbulent narrative. Stalingrad paved the way for Soviet advances Westwards towards Ukraine and elsewhere culminating in the titanic struggle that would be the Battle of Kursk, that truly represented a beginning of the End of the struggle on the Eastern Front in my mind over Stalingrad.

Source: Anthony Beevor: Stalingrad