Years before Spinal Tap, District Nine, reality TV, and a zillion other mash-ups of the documentary, news, and fiction forms, the pioneering Peter Watkins went where his followers still fear to go. In 1964 he invigorated the antiwar movement and scared Britain half to death with The War Game, a deadpan simulated report on a nuclear attack. He followed up in 1971 with the even more confrontative and controversial Punishment Park, which posited citizen kangaroo courts convened to suppress surging opposition to the Vietnam War; imagine a cross between a draft board, Guantánamo tribunal, and red-white-and-blue Star Chamber. Summarily convicted, protesters, radicals, and draft dodgers are offered a choice: 20 years in prison or three days in Punishment Park. It’s capture the flag in hell: cross 53 miles of searing desert without water, eluding the police and guardsmen who train by pursuing they, reach the flapping Stars and Stripes, and they can supposedly go free.

The film, ostensibly shot by a visiting British-German news crew, cuts between Defendant Group 637’s desert ordeal and 638’s screaming trial. Watkins cast nonprofessional actors according to their politics as well as spot-on physical types (watch for Julius Hoffman, Pat Nixon, and Bobby Seale lookalikes). They improvised with such sincere, abrasive, and persuasive passion that some came to real blows.

Punishment Park got lambasted as an anti-American screed on release, but it’s also a patriotic screed; everyone gets a say, and the shaggy young martyrs are hardly saintly. It’s very much of its day, and may make you glad to have missed that time or left it behind. But post-9/11, it does not seem quite so far away. Punishment Park is strident, repetitive, and infuriating, in the way of much political cinema and improvisation. But it’s also hypnotic and, in its gritty way, a tour de force.

Punishment Park shows at Northwest Film Forum July 2-8 at 7 and 9pm.