Forty years ago today, a murky military encounter at sea plunged the United States deeper into the war in Vietnam. On Aug. 2, 1964, three North Vietnamese torpedo boats attacked a U.S. destroyer in the Gulf of Tonkin. Two days later, the U.S. Navy reported to Secretary of Defense Robert McNamara that another American destroyer was under attack by the North Vietnamese.

Those critical events would ultimately lead the United States to send more than a half a million American troops into Southeast Asia.

The attacks spurred Congress to pass the Gulf of Tonkin resolution, which gave President Johnson power to use force in Southeast Asia. With the measure's passage, U.S. involvement in the Vietnam War became legitimized and grew.

In 1964, CBS commentator and TV anchor Walter Cronkite knew only what official reports acknowledged. Four decades later, he offers a perspective on the incident he didn't have at the time.

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