Francis Ford Coppola‘s acclaimed 1979 Vietnam War epic Apocalypse Now may not have been the same without the involvement of the Grateful Dead‘s rhythm section of Mickey Hart and Billy Kreutzmann.

The two drummers, who firmly established their nightly tradition of the exploratory “Drums” > “Space” instrumental portion of Grateful Dead performances beginning in the 1980s, were hand-picked by the film’s director to compose and record their rhythm-inspired music to help bring his creative vision of jungle warfare to life on screen. Although the film arrived in August 1979, 11 recordings on The Apocalypse Now Sessions weren’t released until 40 years ago today on May 25h, 1980.

Related: Mickey Hart Talks Sounds Of The Universe, Dead & Company Plans, Parkland Students [Interview]

As part of the unique recording sessions, non-rhythm musicians were also invited to collaborate on the project, including their Grateful Dead bandmate and bassist Phil Lesh, Brazilian jazz singer Flora Purim, and Sly and the Family Stone drummer Greg Errico to name a few. According to the album’s liner notes, the various musicians composed and recorded their parts while watching a cut of the film in real-time over a period of 10 days at the Club Front recording studio in San Rafael, CA, which also served as the Dead’s rehearsal hall and hangout spot over the years.

It’s worth noting that one of the instruments built for these sessions was a one-of-a-kind creation now known as “The Beam,” Hart’s large, stringed device that sends unparalleled audio sounds out to the farthest depths of the universe. Hart still uses The Beam during the “Space” portion of Dead & Company performances to this day.

Watch Hart discuss the sessions for the album in-depth in an old interview below.

Mickey Hart Talks Apocalypse Now Sessions

[Video: WentworthGallery Shows]

Fans can also celebrate the 40th anniversary of the war-inspired instrumental album in full via the Spotify player below.

The Apocalypse Now Sessions

Scroll down to check out some of the photos from the film project’s recording sessions shared by Hart.