The .357 Magnum was collaboratively developed over a period in the early to mid-1930s by a group of individuals in a direct response to Colt's .38 Super Automatic. At the time, the .38 Super was the only American pistol cartridge capable of defeating automobile cover and the early ballistic vests that were just beginning to emerge in the post-World War I "Gangster Era." Tests at the time revealed that those vests defeated any handgun cartridge traveling at less than about 1000 ft/s. Colt's .38 Super Automatic just edged over that velocity and was able to penetrate car doors and vests that bootleggers and gangsters were employing as cover.