Early in 1944, the German scientists involved in the nuclear energy program, informally referred to as the Uranverein (Uranium Club) under Kurt Diebner, Werner Heisenberg, and other scientific minds had finished the work on their first atomic weapon. Hitler, obsessed with the idea of a city-destroying weapon, poured as much of the Third Reich’s industrial and scientific capabilities into furthering the development. The test of the first weapon occurred that May when the prototype weapon was detonated in Smolensk. The German military pulled back, letting Soviet forces enter the city unopposed. The explosion killed an unknown number of civilians, wiped out most of a Soviet Rifle Corps (estimated to be upwards of 30,000 casualties, but could be as high as 50,000), and finished destroying what was left of the city that was left standing from the 1941 battle.
The Red Army found itself paralyzed for a long time as the STAVKA (Soviet High Command) and the Soviet civilian leadership tried to figure out what to do. Soon, the Red Army restarted the offensive against the hard-pressed German military, but its operations were much more cautious in nature as it feared being attacked by another atomic weapon. The loss of so many soldiers in one action caused Stalin to again demand his allies open up another front in France, fearing that the Allies were willing to allow the Nazi’s to destroy the Soviet Union and allow Russian soldiers to fight the battle for them.
Churchill and Roosevelt, however, feared that the Soviet Union would make a separate peace with Germany and leave the Allies to face Germany alone. General Eisenhower and the Allied military leadership were worried about any landing, as the large concentration of soldiers in such a small area (the beaches of Normandy) would make them very vulnerable to atomic attacks. However despite these worries on June 6th the Allied armies conducted Operation Overlord, landing in Normandy and catching the German military by surprise.
But their luck turned against them, as by D-Day +4 Hitler was finally convinced that this was the real invasion and not a diversion. A modified V-2 made to carry an atomic weapon to England was diverted to strike the beaches of Normandy, where it managed to wipe out thousands of soldiers on the beaches, along with the supplies necessary to keep the Allied forces operating and most importantly the artificial docks, or mulberry harbours, that allowed the Allies to keep unloading supplies without having captured a major port like Cherbourg or Le Havre.
The attack decimated the Allied armies, and the German military soon began pushing the Allied soldiers back towards the coast. The Allies were shocked, and the mood began to turn against the war in the US and UK as civilians worried about a German weapon that couldn’t be stopped. The Manhattan Project was given the highest priority as the Americans tried to rush their own bomb into production, but it wouldn’t be ready until January of 1945.
In July the Germans used a U-Boot to detonate a nuclear weapon in New York harbor, while using another modified V-2 to strike London in September. With hundreds of thousands of civilians dead, the war looked grim for the Allies. Germany turned its murderous rage back on the Soviets, using the next two atomic weapons to hit large concentrations of Soviet soldiers before they could launch major offensives against the German military.
But by 1945 the Americans had their first atomic weapon. Without any time for testing the bomb was dropped on Berlin, killing thousands but failing to catch Hitler. Soon a massive nuclear exchange began, and by the time the summer of 1945 rolled around Europe was in flames. Most major cities were decimated, and the countries began to fragment. Generals in Eastern Europe, lacking any communication to their superiors, began to turn the areas where they were located into mini-fiefdoms as isolated towns and cities soon had to rely on themselves for food and protection. Other soldiers deserted, becoming mercenary groups that began to offer their services to the highest bidder, roving bands of ex-soldiers that no longer had a loyalty to any state.