A special USMC unit was established to be helicoptered into areas where Americans were heavily engaged and under fire.  The casualties were heavy since the enemy was expecting reinforcements.  This small group of 50 Marines knew their chances of survival were not good.

The  book- On Full Automatic: Surviving 18 months in Vietnam- is excellent.   This book will show you how a young Marine got PTSD.  Author Bill Taylor tells it all in graphic detail.  He also notes problems with the early M16 Rifles which jammed and sometimes were not repairable while under fire. 

Go To Amazon and buy the book!!