Is there any actual evidence that shows cranberry juice is helpful in fighting off a UTI?

This is something I’ve heard since I got my first UTI, in college in the 70s. Most recently I heard it from my Doctor’s nurse.
So, is there some ingredient in cranberry juice that helps, or is it just the intake of fluid? I lean toward the intake of fluids….MASSIVE intake of fluids does the trick, really. I have successfully fought off many UTIs with no antibiotics, but just by drinking about a gallon or more of any liquid over the course of a few hours.