Mint condition model 1-5″ made towards the tail end of the availability of the original “Ivorite” material of Westinghouse manufacture.
Brass hilt and Duralumin butt.
This one comes in a model “C” sheath. My guess is it was prudent for the shop to use the standard “C” sheath for a 5.5″ model 15/18 than make a “custom” one off type sheath.
Written on the back of the sheath is 6-02, which one can only assume is when the knife was acquired originally.