Staff Writer (Updated: 6/15/2016):
Total production of S-64 units was 110 beginning with the original S-64 built in three examples. These were followed by six evaluation models for the United States Army as the S-64A. From that came the S-64B which was the civilian-minded version of the Army's CH-54A model and seven were produced. Under Erickson, the line was broadened to include the S-64E and S-64F model marks, these becoming upgraded forms of the CH-54A and CH-54B respectively - the F-model introducing Pratt & Whitney JFTD12-5A series engines.
Civilian market operators of the S-64 are found in Italy, South Korea and the United States. Its primary role is in firefighting where its unique configuration allows the helicopter to carry a considerable water load over uneven terrain, dropping its contents onto raging wildfires with the hope of putting the fire source out.
Production of the military-minded Tarhe yielded 105 total units of its own beginning with the six YCH-54A pre-production models. These were followed by the CH-54A production form which fitted 2 x PW T73-P-1 series turboshaft engines of 4,500 horsepower and 54 examples were built to the standard. The CH-54B saw an increase in overall weight as well as a twin-wheeled undercarriage introduced while power was now served through PW T73-P799 turboshaft engines of 4,800 horsepower. 37 examples were manufactured.
Beyond its service with the United States Army, the CH-54 has been featured by the NASA service of the United States for various program work. In military use, the Tarhe has hauled all manner of heavy objects - from oversized bombs and attack helicopters to combat tanks and cargo containers. A special version even featured skies as its undercarriage.