active because of the ease which active devices can be detected. The most common passive IR device is the
hand-held thermal viewer AN/PAS-7. This piece of equipment is not in the MI battalion or I&S company. This
type of device works on the principle that all objects on earth radiate a certain amount of heat which travels
outward as detectable energy. Because of differences in the amount of heat being radiated by a truck with the
motor running, a man standing near it, and several trees around them, it detects an image of different intensity of
each. Passive and active IR device effectiveness is degraded by heavy rain, snow, or fog.
The AN/PVS-4 (Figures 2-1 and 2-2) is a portable battery-operated, electro-optical instrument used for night
observation and aimed weapons fire. The sight does not emit visible or IR light (except through the eyepiece) that
can be enemy detected. The sight is used on the M16 rifle, M60 machine gun, M67 recoilless rifle, M72A1 rocket
launcher, and M79 and M203 grenade launchers. Mounting brackets are provided for each type of weapon.
Grenade launcher brackets have provisions for super elevation. The range of this sight is 400 to 600 meters (for
man targets) in starlight and moonlight.
The AN/PVS-4 is employed in forward areas as a hand-held NOD to detect, identify, and observe friendly and
enemy operations. A secondary mission is to provide accurate night individual weapon fire. The scope is used
by forward observer, reconnaissance, and ranger units who frequently employ it for final detected target
identification. It may also be used for close up detection at GSR sites. Mounted on, and boresighted to the M16
rifle, it is used for aimed fire.