A ranger is a unit who has received training in observation and marksmanship, they are very brutal and will make the VC wish they were.... well, not VC. Due to their shotguns they are very good at repelling VC ambushes. They are extremely useful for the commander as they can locate hidden VC soldiers from far away and are great when with other men as they can all shoot at the enemy spotted by the ranger. Deadly when combined with sniper or another very high accuracy soldier. The Ranger is also good when attacking the enemy base as you don't need to send your men over the open to the trench and can keep them hidden in the jungle.
The Army Ranger units are what the Army refers to as shock troops. The main duty of the ranger is to go into a combat zone deep behind enemy lines and capture an objective such as a airfield or enemy camp. in Vietnam the rangers took on a variety of missions from search and destroy, to reconnaissance, and as a quick reaction force.
The term Ranger was used already during the beginning of the 17th century. Ranger companies were officially used for the first time during King Philip's War during 1676. They also fought in the American Revolution and the Civil War, War of 1812 and in four French and Indian wars. They are working with normal divisions as reconnaissance battalions.