Mission Galactica: The Cylon Attack (1979) on Netflix

The Battlestar Galactica encounters the Battlestar Pegasus, which they thought to be destroyed. The Pegasus is commanded by one of their most celebrated warriors, Commander Cain. Cain is a strategic genius, but is bent on destroying the Cylons while Adama is happy to acquire fuel and escape, thus keeping his fleet alive to find Earth. When Cain sabotages a mission to obtain fuel, the Galactica and Pegasus are forced to attack a Cylon Base World and three Baseships. While the Galactica stays on to attack the planet, the Pegasus leaves to engage the Baseships (against orders). After the battle, the Pegasus just keeps on going into deep space and is never heard from again. The Galactica gets the fuel they need and the fleet continues its journey, looking for Earth.