These binoculars were mounted to an anti-aircraft gun on a German gun boat. The different shades of lens filters allows for a very dark filter with which the observer could look directly into the bright sun. This is a very important feature as it was a favorite tactic for attacking aircraft to approach with the sun immediately behind, thereby blinding the anti-aircraft units
These Kriegsmarine binoculars were marked blc the code for Carl Zeiss Jena. All lenses are marked T for coated lenses. Early coatings on the lenses allowed for a brighter picture.
The binocular also had moisture absorbent cartridges and nitrogen ports to remove moisture and reduce lens fogging. They were robustly made and very well waterproofed as would be necessary for a shipboard optic.