Formed in 1969 as an offshoot of Students for a Democratic Society, the Weathermen took their name from a line in Bob Dylan's "Subterranean Homesick Blues" ("You don't need a weatherman to know which way the wind blows"). Believing that the only way to end U.S. involvement in Vietnam was to "bring the war home," the Weathermen undertook a series of demonstrations, instigating the "Days of Rage" in Chicago, breaking Timothy Leary out of jail and surrounding the Pentagon. Much of the Weathermen's activism had an air of agitprop theater, but they also plotted to bomb institutions they felt were complicit in the war. Although they insist they sought only to destroy property, one person was accidentally killed in an early bombing, and three Weathermen inadvertently blew themselves up in a Greenwich Village townhouse. The group went underground and led the FBI on one of its most extensive and frustrating manhunts.

Using archival material and present-day interviews, Green and Siegel put the Weathermen in context, not only of the radical-chic ethos of the time but of the international revolutionary movements that were happening simultaneously. Marshaling images of the Vietnam War and the violent suppression of protests at home, the filmmakers make a case for one activist's contention that the Weathermen were taking what they saw as the only conscientious action against an immoral society.

People who witnessed the painful schism in the left created by the Weathermen may feel that Green and Siegel buy into the militants' rationale too uncritically. But the nonconfrontational style has its advantages. The most compelling moments of the film are provided by former Weathermen, including Mark Rudd, Billy Ayers, Bernardine Dohrn and Naomi Jaffe, as they explain, defend, justify or apologize for what they've done.

"The Weather Underground" skillfully limns one of the most wrenching times in American history, but it is as perceptive when it comes to the matters of individual conscience.