What kind of missions did Vietnam snipers do?

During the Vietnam War, US Marine snipers used non-semi-automatic rifles and operated as scouts (reconniassance/military intelligence) as part of their sniper function. US Army snipers used the XM-21 weapons system (M-14 rifle). Priority targets were always key personnel: Leaders, radio operators; more often, for the US Army, the mission(s) consisted of eliminating "sappers". The "term" SAPPER was introduced in WWI for men digging tunnels under fortifications and destroying them with demolitons. In the Vietnam War, the "term" SAPPER was used for enemy personnel (enemy commando's) infiltrating into a US Firebase (crawling through the barbed wire perimeter), AND for enemy personnel planting Soviet/Chicom (Chinese Communist) made land mines. US firepower within the FIREBASE "almost" always terminated the infiltrating "SAPPER" (enemy commando). The remaining "Sapper", whose mission was planting Soviet/Chicom land mines, was normally operating on some distant dirt or paved highway well away from the Firebase. US Army snipers were often sent to wait it out, on those isolated roads, and to terminate them.