This is always a fun topic of conversation. Which weapons in each war helped turn the tide towards victory or defeat, or could have.

To make this easier for all of us, please name the war you're talking about and then the country followed by the weapon. Then tell us all why you think that. That'll make it easier to keep track and make comparisons.

We'll start with the obvious:

World War 2
United States
P-51

It's simple, it made it possible to both destroy the industrial capacity of Germany and also allowed the bombers to double as bait to draw the Luftwaffe into the air to be destroyed.

These actions made it possible for the allies, including the Russians to take full advantage of the production capacity. A war with an unhindered German production capacity would have been a much longer and bloodier conflict, especially for the Soviets.