Considering that there's been multiple cases of almost-oops-nukewar...<p>If you are offered the opportunity to go back in time and, say, kill Hitler, don't take it. You might come back to "Threads".<p>This is something that the film remake of "The Time Tunnel" left out. (The film is pretty OK.) If you really did have the ability to change the past, you'd need to be prepared to come back to a post-nuclear wasteland. So, your facility would need to have access to enough power generated on-site that you could keep going back and changing things (once? twice? thrice?) until you get it right and we're back to our world where the world wars haven't (yet) gotten past Number Two.