James L. Lager (1993), Leica. An Illustrated History. Vol I- Cameras, p. 161-164.
Lager states that the X-Ray Leica was used in the early part of World War II for the purpose of conducting medical examinations during war mobilization. Manufactured by E. Leitz, New York, the camera was fitted with a fast Xenon lens and used to photograph the x-ray fluroscope screen. Many of the cameras carry a distinctive W.oX. engraving for the supplier - the X-Ray Division of Westinghouse.
The New York X-Ray cameras illustrated by Lager all carry a two or three digit serial number prefixed by N.Y., whereas this camera has the six digit serial number of a 1938 Standard. The Leica Roentgen, Leitz Wetzlar's version of the X-Ray Leica, used a 24 x 24mm. format and was usually engraved with a prefix R.
This camera may be a postwar conversion.