Ending is from 1968's 'The Party' with Peter Sellers
Since a lot of folks have posted about the ending I thought I would point out where it came from.
If you rent the 1968 MGM (same year and studio as Hell in the Pacific) Peter Seller's film "The Party", you can see the explosion from the end of this movie. It occurs at the beginning when Sellers accidently blows up a movie set.
I heard that the studio did not like Boorman's introspective ending and just crudely spliced in the explosion from the Peter Sellers film.
In Japan they saw the original ending that is available on some dvds and the old laserdisc.
Hope this helps