Congress considers the Vietnam Era to be “The period beginning on Feb. 28, 1961 and ending on May 7, 1975 … in the case of a veteran who served in the Republic of Vietnam during that period,” and “beginning on Aug. 5, 1964 and ending on May 7, 1975 … in all other cases.”

That’s according to the document, “U.S. Periods of War and Dates of Recent Conflicts,” prepared by Congressional Research Service for members and committees of Congress.

Why those dates?

The beginning: According to the New York Times, in 1996 Congress recognized the start of U.S. involvement in the Vietnam War as Feb. 28, 1961, when U.S. military advisers began accompanying South Vietnamese troops on operations.

The war’s start was formerly established as Aug. 5, 1964, when President Lyndon B. Johnson reported that North Vietnamese gunboats attacked two U.S. Navy destroyers in the Gulf of Tonkin.

The end: While the United States withdrew troops from Vietnam in 1973 after the signing of the Paris Peace Accords, U.S. involvement in the Vietnam War did not end until the fall of Saigon on April 30, 1975. Two Marines — Cpl. Charles McMahon, 21, and Marine Lance Cpl. Darwin Lee Judge, 19 — were killed in a rocket attack the day prior to the evacuation from Saigon.

Congress considers May 7, 1975 to be the end of the Vietnam War for the U.S.,  because on that date President Gerald R. Ford announced that the Vietnam Era had ended.