Though capturing a heavily  reinforced Moscow was no longer tenable in early 1942, oil fields in the south remained a tantalizing objective. Adolf Hitler’s maniacal ambitions depended on such resources to support his military operations and war industries, and by June, another massive Axis army was on the march towards the rich oil fields of the Caucasus.

With fast-retreating Soviet troops yielding considerable ground, an opportunity emerged to seize control of the Volga River, a key artery in the Soviet war economy. The German Sixth Army, numbering some 250,000 men, wheeled away from the main advance and drove toward Stalingrad, an industrial city perched on the banks of the Volga. Soviet leader Joseph Stalin, unsparing as always, issued a decree demanding the defense of his namesake city to the last man, setting the stage for one of the most epic and desperate struggles of the war.

The Germans began by unleashing a firestorm of incendiary bombs and artillery shells that turned the urban enclave into a smoldering wasteland. Piles of rubble filled the city streets and prevented German armor from maneuvering, forcing German and Soviet foot soldiers to battle block to block. By November, Stalingrad was mostly in German hands.

A stunning reversal soon unfolded. Just as the Soviets were nearing collapse, the Red Army launched a surprise counterattack outside the city, surrounding the Sixth Army and trapping the Axis troops in a large pocket, cut off from supplies and reinforcement. Day after day, the Soviets poured artillery fire into what came to be known as “the cauldron,” and as winter settled in, temperatures plunged once again. By February, with just 91,000 of his beleaguered, frostbitten men left alive, Field Marshal Friedrich Paulus had no choice but to defy Hitler’s wishes and surrender what was left of his starving army.

Despite the crushing defeat at Stalingrad, Hitler was not through in the East. In the summer of 1943, a large Soviet army made a deep penetration of the German lines near the town of Kursk.

The thrust created a large bulge, or salient, in the lines that exposed the advancing Soviets to German forces on three sides. The Germans intended to strike with 400,000 men and 3,000 panzers, but Hitler intervened, postponing an attack on the salient until newer model tanks could be delivered from Germany.

The Soviets took advantage of the pause, marshaling reinforcements and transforming the salient into a stronghold defended by more than one million troops and 3,300 tanks and armored vehicles. The Battle of Kursk became the largest tank battle in history and a bloodbath for both sides, with the Soviets alone suffering more than 750,000 casualties.

German losses were equally staggering, and their inability to defeat the Soviets marked yet another strategic failure for Hitler on the Eastern Front. From that point on, the fighting on Soviet soil became a purely defensive struggle for the Germans, and the start of a long westward retreat.