The Twilight Zone - No Time Like The Past

Paul Driscoll doesn't much like the way the 20th century has developed thus far and decides to go back in time to change mankind's future. He first travels to Hiroshima and tries to warn an English-speaking policeman of what is to come, but to no avail. He then travels to Nazi Germany and attempts to assassinate Adolf Hitler but is thwarted when his rifle misfires. He then finds himself aboard the Lusitania but again is unable to convince the ship's captain to alter course before it is torpedoed. When he returns to the present, he agrees with his colleague Harvey that the past cannot be changed. He still doesn't like the present and so decides to back to July 1881 and live his life in the small town of Homeville, Indiana. Unfortunately he learns yet again that past events cannot be changed.