Very, very slowly with the introduction of "military advisors" and CIA pilots in support of the French. By 1960 there was a 12,000 member US force in Vietnam. This was all in place before the first combat units were sent in.
The first advisers went to Viet Nam when Eisenhower was president. Soon after President John F. Kennedy sent military advisors. US forces in Vietnam began to grow slowly. By the time President Johnston was in office, the US troop build up was accelerated. Before Johnson decided not to run for reelection in 1968, the US had as many as 500,000 troops in Vietnam.
Eisenhower continued the U.S. in the fighting. Kennedy, Johnson, and Nixon also served their terms during the war. Harry Truman said to me that Charles De Gaulle, acting as representative of France, requested that the United States of America fulfill their(USA) duties under the mutual assistance treaty passed by the Senate of the United States Of America and signed by Franklin Roosevelt;so, Harry Truman sent US soldiers and other aid to South Vietnam as requested by France in their defense. To further help to understand the answer to this question, I say that each election opposition candidate for President of the United States did state that their opponent started the Vietnam War;so, many leaders into the Vietnam War.
Presidents Eisenhower & Kennedy initiated US Military involvement in South Vietnam in 1955. President Johnson (LBJ) initiated US military involvement with NORTH Vietnam in 1964 (Operation Pierce Arrow-a jet airstrike against North Vietnamese NAVY Torpedo Boats stationed there). This was in response to the Tonkin Gulf attack (Incident in cold war parlance). Presidents Nixon & Ford inherited LBJs legacy.
The United States went into war with Vietnam in the year 1965.
That was President Lyndon Johnson.
President Eisenhower sent US Military Advisers to South Vietnam in 1955.
President obama
President Carter did not support the amnesty for men who left the US to avoid the draft during the Vietnam war due to his will to win the war and defeat Vietnam.
The US had military advisers in Vietnam under Kennedy, but the was did not really start for the US Johnson became President.
President Eisenhower sent US troops to Vietnam in 1955, President Ford pulled out the last US troops in 1975.
President Eisenhower sent US advisers to Vietnam in 1955. President Kennedy sent US Special Forces (Green Beret) to Vietnam in 1961. President Johnson sent US regular forces to Vietnam in 1965.
President Johnson believed that the US could defeat north Vietnam because the US had won WWII with firepower, and the US had the most firepower on earth during the Vietnam War.
President Gerald Ford
Eisenhower
Nixon.
lyndon b. Johnson
The United States went into war with Vietnam in the year 1965.
In the 1950s and 1960s Eisenhower and Kennedy sent US soldiers to South Vietnam. In 1965 President Johnson sent the US Marines.
US Ambassadors did not believe Diem would accomplish US goals in Vietnam.
John F. Kennedy was President. 1960 to 1963