The H-21 "Shawnee" was used by the US Army early in the Vietnam War era. It was mainly used as troop-transporter and was armed with a M37C cal. 30 or M2 cal. 50 machinegun.
The helicopter was also used to sling-tow various loads like M101 artillery pieces etc.
The CH-47A was first used in Vietnam in 1962 and was an US Army heavy lift helicopter. It was armed with two M60 machineguns as doorguns.
It was use for troop or cargo transport and could sling-tow various loads like fueldrums etc.
The helicopter was also use to recover downed aircrafts. Some CH-47A like the one named "Pipesmoke" were nearly only used for this purpose.
The CH-54 was also called "Skycrane" and was an US Army heavy lift helicopter. It was used to sling-tow heavy and bulky loads, recover aircrafts or carry various cargo in a specially designed container.
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All infos and pictures are gather from various sources found in the net. I tried to use pictures that are not explicitly copyright protected and resized/reworked some of them to fit this short overview.
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