In October 1961, top Kennedy aides General Maxwell Taylor and Walt Rostow visited South Vietnam to assess the deteriorating military situation there. “If Vietnam goes, it will be exceedingly difficult to hold Southeast Asia,” Taylor reported, advising Kennedy to expand the number of US military advisors and to send 8,000 combat soldiers.
Defense Secretary Robert McNamara and the Joint Chiefs of Staff instead recommended a massive show of force by sending six divisions (200,000 men) to Vietnam. However, the President decided against sending any combat troops.
President Kennedy letter to President Diem, 14 December 1961, The Pentagon Papers, Gravel Edition, Volume 2, pp. 805-806
President Kennedy then sent additional military advisors along with American helicopter units to transport and direct Army of the Republic of Vietnam (ARVN) troops in battle, thus involving Americans in combat operations. Kennedy justified the expanding US military role as a means “…to prevent a Communist takeover of Vietnam which is in accordance with a policy our government has followed since 1954.” The number of military advisors sent by Kennedy eventually surpassed 16,000 men.
REFERENCES AND FOOTNOTES:
 Source: Department of State, S/S Files: Lot 66 D 219. Secret. Also printed in Declassified Documents, 1981, 591A. A copy of the report was transmitted to McGeorge Bundy on July 11 with a note that the programs and momentum generated by the Task Force would be continued by a new Working Group on Vietnam under the newly created Task Force on Southeast Asia. https://history.state.gov/historicaldocuments/frus1961-63v02/d233 President Kennedy letter to President Diem, 14 December 1961, The Pentagon Papers, Gravel Edition, Volume 2, pp. 805-806.