Photographer Nacio Jan Brown captured a moment that shocked many: a National Guard helicopter spraying tear gas on students and antiwar protesters in Cal’s Sproul Plaza on May 20, 1969 — in some sense extending “the front” from Vietnam onto college campuses.

The juxtaposition of the military-grade helicopter with the Campanile — the unofficial symbol of the UC Berkeley campus — helped make this photograph an iconic image of the suppression of campus protest.

The demonstrators had gathered to commemorate the death of James Rector, who had been shot by police while on the rooftop of Granma Books on May 15, during a protest over the disposition of People’s Park.