The AN/PAS-4 was an early infrared weapon sight for the M21 rifle and is the last infrared scope fielded for combat use in Southeast Asia. Its principal components are the 4.5X telescope, 124,000 candlepower IR light source, and 6 volt Sonotone nickel-cadmium rechargeable battery (see battery section). The scope system was manufactured by Polan Industries or Varo Manufacturing Co. Inc. The entire system weighs just over 12 pounds. Later starlight scopes intensified low levels of ambient light were found to be more suitable in most conditions, however the active light source provided by the AN/PAS-4 was superior when there was no ambient light at all.
This unit was manufactured in 1967 by Polan Industries and has survived in mint condition. See "The Long Range War" by Peter Senich pg 223 for more info.