Does look like a military piece of equipment, so I guess it's possible it's a Grenade Launcher site, but it seems a bit elaborate for that purpose. M203 sights don't have a level.
That empty space looks just right to snap in an lensatic compass. The leveling feature makes me think it was probably used by Forward Observers for the Field Artillery. Looks like a WWII - Vietnam era Army issue piece of equipment.
Those really old B&W Cartoons are - for me anyway - just nauseating to look at. There's just something WRONG about them, from the drawings to the music to the dialog to the "bounciness" of the character. I feel like if I watch too long I'm going to get sucked into the Twilight Zone and spend all eternity with Kevin McCarthy....
That empty space looks just right to snap in an lensatic compass. The leveling feature makes me think it was probably used by Forward Observers for the Field Artillery. Looks like a WWII - Vietnam era Army issue piece of equipment.