Telescope Mirror Unit or Lens Mirror Military? Robust. New Old Stock on mount

Description

i did not want to polish front surface ? mirror but the bit you see is surface skin oil or ? NASA ROR should take it right off.  no idea what this was for.  heavy
On Aug-14-21 at 21:44:13 PDT, seller added the following information:
Mirror is fractionally shy of 6" across (Diameter) may be more accurate than my Staples Wood Ruler but...