The AN/PVS-1 was the first starlight scope fielded for combat use in SE Asia. This unit was manufactured an 1967 and is one of 2000 manufactured by Electro Systems. The principal component of the AN/PVS-1 cops is the 25mm cascade 3-stage image intensifier tube designed and manufactured by Varo Inc.
The AN/PVS-1 was very effective for its time and in good ambient light conditions in detecting enemy fire and movement at ranges of 200-500 yards particularly near reflective bodies of water. Although the optical system was very durable the image intensifier tube internal mechanical components were very sensitive to the positive recoil of the M-21 rifle and were often damaged as a result. A repair of this nature was a delicate operation that was not performed in the field.