A U.S. Army Vertol CH-21C <i>Shawnee</i> (s/n 56-2133) in flight.
U.S. Army
U.S. Army photo from the official U.S. Department of the Army publication <i>Vietnam Studies - Airmobility 1961-1971.</i> Washington D.C. 1989 <a rel="nofollow" class="external autonumber" href="http://www.history.army.mil/books/Vietnam/Airmobility/airmobility-fm.html">[1]</a> photo <a rel="nofollow" class="external autonumber" href="http://www.history.army.mil/books/Vietnam/Airmobility/p270.jpg">[2]</a>