Donald Duncan was a patriot who wanted nothing more than to serve his country. He volunteered and spent two tours in Vietnam as a Green Beret. But what he saw horrified him. In February 1966, after he resigned from the service in disgust, Duncan penned an article in Ramparts that revealed widespread torture of civilians and indiscriminate bombing of Vietnamese targets, and exposed the distortions of the Pentagon's propaganda machine.

It was a courageous act that helped spawn a 'GI movement': In spite of popular legend, the antiwar movement's vanguard was not college students or veterans, but active-duty soldiers like Duncan who resisted the war.

They organized demonstrations and refused orders to fight. They published underground newspapers and hung out at radical coffee shops near military bases, where they provided support to comrades returning from Vietnam or shipping out. A new documentary, Sir! No Sir! (www.sirnosir.com), opening in March, tells their stories.

Filmmaker David Zeiger worked at one of those coffee shops and wanted to document what he'd seen but feared that audiences were tired of Vietnam movies. Then came the Iraq war. 'George W. Bush's declaration of war on the world and the horrendously criminal assault on Iraq made the film feel very necessary,' he says, 'and, ironically, has created an audience for it.'

Most striking about the film is the sheer size of the GI movement, which showed up for every major peace march from 1965 to 1972. The underground GI press swelled to more than 100 newspapers. Thousands flocked to Jane Fonda's FTA tour, an antiwar alternative to Bob Hope's USO fare. (FTA was code for 'Fuck the Army,' a spoof of the Army slogan 'Fun, Travel, and Adventure.') According to Pentagon records, there were 503,926 'incidents of desertion' between 1966 and 1971.

Opponents of the Iraq war could learn from the creative actions of the GI movement -- like Armed Farces Day, an annual march that drew thousands of soldiers into the streets to mock the Pentagon brass. Another was the Stop Our Ship Referendum staged by sailors on the U.S.S. Constellation, who invited citizens in the carrier's home port of San Diego to vote on whether the boat should set sail for Vietnam (they overwhelmingly voted no). And in answer to literature drops over Vietnam, Susan Schnall, a Navy nurse, arranged a small plane to drop leaflets promoting an antiwar rally onto Bay Area military bases.