Battlestar Galactica (here meaning the mini series that launched the show, not the 4-season show itself) is based around an extremely large battleship/carrier spaceship and the crew that serves on her.  The Galactica is a vessel more than 50 years old, and was built during a time when humanity was in a life or death struggle with the Cylons—a species of sentient AI and robots.

And, as usual with these reviews:

The Cylons haven’t been seen since the end of that war, and the Galactica is one of the few ships from that time still operating.  It’s seemingly backwards and simple technology was dictated by the enemy.  Cylons were able to hack into and take over any networked device, which meant that only the simplest weapons could be used to fight them.

We catch the Galactica just at the end of its life, as it’s about to be decommissioned and turned into a museum.  It is at that moment that the Cylons strike humanity again by firing nuclear weapons at every major city in the 12 Human Colonies.

The entirety of Humanity’s army is quickly scrambled to fight the Cylons, but they have infiltrated the networks that run all of the current weapons and ships that Humanity has available.  By the end of the first episode, only the Galactica (that survived due to it’s old design) and a small flotilla of civilian ships has survived.

The Galactica and its crew then spend the rest of the miniseries attempting to fight their way out of the Cylon ambush to safety.