What does that have to do with anything? Hitler didn't use the V1's and V2's to attack military targets. Sure, if he had successfully launched heavy V2 attacks against southern England the D-Day forces would have been weakened, but the rockets weren't even used for that. Though it was speculated that the rockets could have contained biological or nuclear weapons, no V1 or V2 rocket was ever equipped with either. They were sent against British population centres in retribution for the massive Allied bombings against Germany. Also, I'm sure you know that the V2 rocket later had mobile launching stations that were positioned within range of England and Northern France until several months after the D-Day landings.
The German army was weakened by one million men in 1941 against the Soviet Union. In 1942, it lost the entire 6th Army - among the best and most professional units of the Wehrmacht - at Stalingrad, along with enough equipment to supply a third of the whole German Army. Shortly afterwards, the Germans regrouped and counter attacked. The Waffen SS was able to recapture Kharkov, the fourth-largest city in the Soviet Union. This provided a tantalizing taste of what could be accomplished through mobile war.
Hoping to repeat his success at Kharkov, Hitler ordered 'Operation Citidel' to be carried out against the Kursk salient in 1943. Nearly one million German soldiers were massed for the attack, as were most of the new German tanks such as the Tiger, Panther, and Elephant. However, he waited too long to build up forces, thusly allowing the Soviets time to build massive defenses (since they were well aware of the German plans).
The Germans were effectively destroyed at the Battle of Kursk. After that battle was lost, the Germans lacked the strategic reseverves to launch another major attack in Russia. With the initiative now definitively transferred to the Soviets, the German army could hope to do no better than to 'stem the Red Tide.' They were failing to contain the Russian advance for at least a year before D-Day, which did little more than to compound an already fatal problem.
D-Day was followed up by Operation Market-Garden, which was a spectacular failure. Had it not been for the German offensive in the Battle of the Bulge, the Germans could have held the Western Allies off for another six months at least. The failure of the Battle of the Bulge was due mostly to the shortcomings of the Wehrmacht as a result of 3 and some years of war with the Soviets, who by now had also cut off the Germans' main oil supply at Ploesti. The shortage of, and eventual total lack of fuel was the critical blow to the Germans in the Battle of the Bulge.
The Soviets were granted the responsibility of taking Berlin, by the way, and the Germans certainly would not have surrendered until Berlin fell. The Soviets lost 100, 000 men to take that city alone, which would have been devastating casualties to the Western Allies.
America unequivocally won the war with Japan, but the war in Europe was won more by the Soviets than any other combatant.