The Imperial Fleet was always complete for the Galactic Empire the moment you saw a TIE Fighter. It is a major symbol of the empire and is heavily connected to the Sith. They are carried aboard Star Destroyers or battle stations and one pilot could operate it cleanly at blazing speeds. This spacecraft actually used twin ion engines to operate too. For many years, that was the biggest science fiction part of the TIE Fighter. Yeah, we could make a real version of it but those engines? NEVER!
Today, ion engines exist and we actually use them on several space-traveling robots. They do not use up energy at a fast rate, so they are incredibly efficient, but do take a while to charge up. We charge them by using solar panels to literally capture solar energy. TIE Fighters, you’ll notice, are equipped with many solar panels themselves. Of course, these ion engines do not work exactly the same. It takes quite a while for them to get to a relatively fast speed and any slow-down would take them longer to rise in speed. Therefore, they would not be a great engine to use for a speedy spacecraft.