Breaking the My Lai Massacre Story: In November 1969, Hersh tracked down William Calley at Fort Benning after receiving a tip about a lieutenant being charged with murdering civilians. Hersh interviewed Calley and other soldiers, piecing together the full horror of the March 16, 1968 massacre. When major media outlets declined the story, he distributed it through the small Dispatch News Service.

Pulitzer Prize for International Reporting: Hersh won the 1970 Pulitzer Prize for International Reporting for his My Lai coverage. He followed up the initial story with a series of articles and two books, "My Lai 4" (1970) and "Cover-Up" (1972), that exposed the full extent of the massacre and the military's systematic concealment.

Exposing CIA Domestic Spying Operations: On December 22, 1974, Hersh published a front-page New York Times article exposing a massive illegal domestic espionage operation by the CIA, codenamed Operation CHAOS. The program had spied on hundreds of thousands of American citizens, including anti-war activists, civil rights leaders, and journalists, in direct violation of the CIA's charter.

Abu Ghraib Prisoner Abuse Expose: In April 2004, Hersh published a series of articles in The New Yorker revealing the systematic torture and abuse of Iraqi prisoners at the Abu Ghraib prison by U.S. military personnel. His reporting, accompanied by the release of graphic photographs, exposed a pattern of prisoner abuse authorized at the highest levels of the Bush administration.

Government Retaliation and Pressure: Throughout his career, Hersh faced persistent government pressure, legal threats, and attempts at retaliation for his reporting. After the My Lai story, the military and Nixon administration attempted to discredit him. Following the CIA story, intelligence officials tried to undermine his credibility. After Abu Ghraib, the Pentagon launched an aggressive campaign against his reporting.

Creating the Modern Accountability Journalism Template: Hersh's methodology of cultivating deep sources within government and military institutions, combined with relentless documentary verification, established the modern template for investigative accountability journalism. His approach influenced generations of reporters including Bob Woodward, Dana Priest, and James Risen.

Controversial Later Reporting: In his later career, some of Hersh's reporting became controversial, including claims about the killing of Osama bin Laden and assertions about chemical weapons use in Syria. Critics argued that some claims relied on anonymous sources that could not be independently verified, while supporters maintained that Hersh continued to challenge official narratives.