Riverine Warfare

In July 1965 the staff of the United States Military Assistance Command, Vietnam (MACV), teas drafting the campaign plan for 1966, the purpose of which was to help the government of South Vietnam establish control over the people. The staff concluded that it was possible to secure government control over the I, II, and III Corps Tactical Zones, a conclusion largely based on the presence of American and other Free World Military Assistance Forces in these corps areas. In the IV Corps Tactical Zone, however, where there were no U.S. ground forces to bolster the efforts of the Vietnam armed forces, the staff questioned whether the objective of the campaign plan could be attained. The armed forces of Vietnam were considered capable of maintaining their position in the IV Corps, but not of reducing Communist control over significant portions of the population and terrain in the Mekong Delta. While additional American and other Free World Military Assistance Forces were planned for the other corps areas, none were planned for the IV Corps area. In the opinion of the staff, there could be no substantial progress in the IV Corps Tactical Zone unless U.S. ground forces were introduced.

http://www.history.army.mil/books/Vietnam/riverine/chapter2.htm