<P> In Hanoi, Soviet Premier Kosygin announced the Soviet Union had agree to assist North Vietnam to defend itself from air attacks, by providing surface - to - air missiles (SAMs), jet fighter planes, technical support and advisers . </P> <Dl> <Dt> 13 February </Dt> </Dl> <P> President Johnson approved Operation Rolling Thunder, the Joint Chiefs of Staff plan for the sustained bombing of North Vietnam . Over an 8 - week period, U.S. warplanes planned to bomb fixed targets and interdict military traffic along roads in southern North Vietnam . Johnson did not immediately launch Rolling Thunder . </P> <Dl> <Dt> 16 February </Dt> </Dl>

How many us combat troops were in vietnam as of march 8 1965