Developed in 1952, the Kaman K-600 is a larger and more powerful version of the HTK-1.  The cabin has a capacity of 5 passengers, including the crew.  The U.S. Air Force designated it the H-43A (now known as HH-43A), equipping it for firefighting with a 1000 lb (450 kg) fire fighting kit and small skis [1].  Designation under the U.S. Marines is HOK-1 (now the OH-43D); under the U.S. Navy, it is HUK-1 (redesignated UH-43C).  The H-43 went into service in April 1958 and was the primary helicopter for firefighting and short range rescue during the Vietnam War [2,3].

Source 1:  Alex, Ralph P. "Helicopters from 'A to Z', Part III". American Helicopter Society Newsletter, Vol. 7, 1961. Page 4-5.

Source 2:  Moorman, Robert W. "Coming Full Circle". Vertiflite July/August 2015. Published by AHS International. Page 19.

Source 3:  Hirschberg, Michael. "The American Helicopter" (2000). Page 58.