The first hot shoe flash appeared for the pre-WWII UniveX Mercury camera. In those days before compact electronic flashes were available, the camera provided the correct sync for appropriate flash bulbs.. The first version of the Mercury flashe used a battery that may be unavailable today. The second pre-war version and the final post-war version used standard penlight batteries. These flashes may be too scarce today to be really practical. The camera was unique in several ways. The simple rotary focal plane shutter (1/20 - 1/1000 second!) was reliable and more accurate than conventional shutters then and perhaps today. However, the competing Argus C3 had a coupled rangefinder, and looked more like many cameras of that time. It's fans may not have cared about the Mercury's far better construction. Despite cutting the Mercury II price in half, the Argus C3 easily became America's first choice for a rather inexpensive 35mm Camera.