http://www . realwarhistory . com The first American combat troops in Vietnam were Marines . They started to arrive in March of 1965 . By October , the 173rd Airborne and the 1st Air Cavalry were there , and they bought their choppers with them . By the end of December , total US strength in Vietnam had jumped from 23 , 000 to 181 , 000 men . And everywhere the low rhythmic pulse of whirling blades echoed throu . . .