We haven’t heard much from Elstree 1976, the fascinating documentary about the many, many actors who had the luck of appearing in one of the most popular movies of all time... but without ever showing their face on-screen. Now, there’s finally a new trailer and a release date.

Elstree 1976 will appear in theaters and on demand on May 6, 40 years after its subjects donned Stormtrooper masks and alien costumes to help populate the Star Wars galaxy. The documentary examines them—as well as the franchise’s most famous unseen star, David Prowse, the man inside Darth Vader’s imposing outfit—and how their participation in what must have appeared to be a goofy, obscure scifi movie has changed their lives. It looks like a must-watch for anyone interested in learning more about how Star Wars got made, especially before it became the pop culture juggernaut we know today.