(covers information from several alternate timelines)
The V-2 rocket was Hitler's vengeance/victory weapon which he used upon Great Britain in 1944 during Earth's Second World War. Ultimately, however, these weapons were used too late to have any affect on the outcome of the war.
In an alternate timeline, the Na'kuhl fanatic Vosk traveled backwards in time to aid the Nazi forces in their conquests, making the use of the V-2 rocket unnecessary. (ENT: "Storm Front", "Storm Front, Part II")
In another alternate timeline, created by the continued living of Edith Keeler, Germany was permitted to complete its heavy water experiments, allowing them to be first in developing of the atomic bomb. This, together with the V-2 rocket, enabled Germany to capture the world, ultimately erasing the Federation. (TOS: "The City on the Edge of Forever")