Definitely cool!
These were the first real night vision devices fielded by the US military. They were developed primarily as a countermeasure to Japanese tactics of nighttime infiltration of defensive positions, and introduced in the latter half of the war. This system on the M1 Carbine was also used during the Korean War. By Vietnam technology had improved so that active illumination was no longer required, though the Starlight system of the Vietnam era did still require a lot of ambient moon and star light to be useful.
More on this early example of night vision:
http://ugca.org/07jan/night.htm