From Wikipedia
For general release in 35mm, Coppola elected to show the credits superimposed over shots of Kurtz's base exploding.[29] Rental prints circulated with this ending, and can be found in the hands of a few collectors. However, when Coppola heard that audiences interpreted this as an air strike called by Willard, Coppola pulled the film from its 35 mm run, and put credits on a black screen.

I uploaded this same scene with FFC's commentary a couple years ago, got a request for this upload with the original audio.