Vietnam Conflict

For a great timeline of the American involvements, see the PBS Vietnam Online site and their Battlefield timeline. The Vietnam Archive Operations Database is an excellent source for information about all operations. The Vietnam War Commemoration site has extensive timeline information. Wikipedia links are included for the addition level of information and reference lists. 
Some of the significant events include:

Operation Ranch Hand, 1962-1971 [to clear vegetation]  (Wikipedia info)

Gulf of Tonkin, 1964 (Wikipedia info) 

Operation FLAMING DART, 1965 (Wikipedia info)

Operation MARKET TIME, 1965 (Wikipedia info)

Battle of Khe Sanh, 1968 (Wikipedia info)

Hue Massacre, 1968 (Wikipedia info)

My Lai Massacre, 1968 (Wikipedia info)

Operation STARLITE, 1965 [1st major battle] (Wikipedia info)

Battle of Ia Drang Valley, 1965 (Wikipedia info)

Operation HARVEST MOON, 1965 (Wikipedia info)

Operation ROLLING THUNDER, 1965-1968 [bombing offensive] (Wikipedia info)

Operation CRIMP, 1966 [largest operation] (Wikipedia info)

Operation UTAH, 1966 (Wikipedia info)

Operation JACKSTAY, 1966 (Wikipedia info)

Operation ABILENE, 1966 (Wikipedia info) 

Operation HASTINGS, 1966 (Wikipedia info)

Operation PRAIRIE, 1966 (Wikipedia info) 

Operation CEDAR FALLS, 1967 (Wikipedia info)

Operation JUCTION CITY, 1967 (Wikipedia info)

Operation BLACK SHIELD, 1967 (Wikipedia info)

Tet Offensive, 1968 (Wikipedia info)

Operation BOLD MARINER 1969 (Wikipedia info)

Operation DEWEY CANYON, 1969 (Wikipedia info)

Operation MENU, 1969 [bombing in Cambodia] (Wikipedia info)

Operation Lam Son 719, 1971 (Wikipedia info)

Operation LINEBACKER I, 1972 (Wikipedia info)

Operation LINEBACKER II, 1972 (Wikipedia info)

Easter Offensive, 1972 (Wikipedia info)

Paris Peace Accords, 1973 (Wikipedia info)

Fall of Saigon - 1975 (Wikipedia info)