What is this?

This scope was given to me 50 years ago by a great uncle who enlisted at age 14 and spent the next 38 years in the navy, mostly as a CPO. He was a gunners mate, diver and torpedo man. He designed 3 torpedo heads used by the navy during his career. Any help in identifying this scope is appreciated.

Strange one; are there no identifying marks or graphic stampings? It appears to be telescopically adjustable with a focusing eyepiece. The brass ball mid-tube leads me to believe that it was mounted in some type of gimbal mount with limited movement. Definitely special purpose