Via the 1964 Shure Microphone Catalog:
The Wilcox Gay Record CR81A and Revere CR81 microphone model is a hand-held unit, ideal for general purpose use in tropical countries and in all coastal areas where heat and humidity are a problem. The microphone was for reel-to-reel tape recording and was supplied with vintage Revere tape recorders. The “CR-81” provides the ruggedness, clear reproduction and high output for public address, communications and recording where high speech intelligibility is vital.
It is recommended for Announcing; Mobile Public Address Systems; Communications; Home Recording, and High Quality Intercommunication. The “CR 81″ can be used either Indoors or Outdoors, fits snugly in the hand, sits firmly on a desk. High impedance. Frequency response 100 to 7000 cps. Furnished with 7 ft. shielded cable. Tan metallic finish. Die cast case. Furnished with stand adapter. Dimensions: 2%” wide, 3’1•” high, 1’12” thick. Model 510 Series designed to be used with S34B or S36A Desk Stands.