The cast of Oliver Stone’s 1986 Vietnam classic Platoon heartily exchange old war stories in this making-of documentary by two of their own: Paul Sanchez, writer-director here, played Doc in Platoon and Charlie Sheen (“Chris”), who has been deployed to provide occasional narration. While Sheen had spent time in outh-east Asia before, accompanying dad Martin on the set of Apocalypse Now, he impresses on us just how inexperienced the rest these “no-name grunts” were.

It was up to Stone’s fellow Vietnam vet, Captain Dale Dye to turn 33 drama school slackers into a trained rifle platoon with a two-week boot camp. Did he succeed? Let’s just say that Tropic Thunder, Ben Stiller’s 2008 Hollywood satire, has a new ring of truth to it and 30 years on, only the level-headed Willem Dafoe can find the line between experiencing actual combat and shooting a movie without catering.

They have, however, authentically captured the 1am atmosphere at a veteran’s bar. Every anecdote is overlong, any point worth making is made seven times over and occasional non-sequitur gems float above the relentless bed of juke-box rock. “It’s Cher, walking into my funeral parlour, and I’m going to do some low-budget piece of shit halfway around the world …” moans John C McGinley. “So I unzipped the old fly and pulled out the old friend and, yeah, I was gonna urinate on Oliver,” chuckles Johnny Depp.

Stone himself never makes an appearance. That’s probably for the best, since the cast clearly despised him. His torturous methods involved forcing actors to do 30-plus takes for a single line of dialogue before revealing there was no film in the camera, and never had been. Then again, after sitting through 90 minutes of their self-indulgent reminiscence, you might conclude they fully deserved it.

• Available on digital platforms from 5 October.