For those not familiar with the TV Show Dr Who, the main protagonist is an alien from the planet Gallifrey. They built your typical highly evolved society which mastered the secrets of the time and in particular of time travel: they are finally known as the Time Lords.

Unfortunately for them, the Daleks, a martial alien society also achieved a control of the time. The Daleks are pretty vindictive. They essentially want to exterminate all life. This build-up to to a war known as the Last Great Time War.

Now I very much like this idea to push on the limit of science fiction into one of the most complex branch: time travel. But then I am not really satisfied by the answer provided by the show runners about the outcome of that war. And I think it could be interesting to take up on that idea for a fiction (or RPG).

Now, as in-universe, the time travel can be accomplished with special ships which require a very specific core. The show isn't very specific on it, but essentially the ships travels a certain vortex which lead the ship to the desired time and place. Small changes can be done: like it's OK to save the life of one of the victim of a tsunami. Larger changes are prohibited: the typical killing your grandfather, or stopping the tsunami as a whole. If said restriction are overlooked, the reality may break, ending all existence. Some say it might open to parallel worlds. In any case, we usually refrain from experimenting with it. The importance of the events is known to the time travellers (as part of their trainings) so they don't erase reality by mistake.

Each of the two species have their technology, but we might consider them equivalent. Weapons are mostly near-futuristic.

Problem is which tactics can be used effectively?

Typically someone who knows the future is used in battles to rewind time again and again. But if both opponents can do the same, what do you do?

How can such a war end on a victory for one side?