I've recently been reading some of the short stories of Dashiell Hammett featuring the Continental Op. These stories were written in the 1920s and are about a detective investigating crime in and around contemporary San Francisco.

I noticed that the characters frequently use the word machine to mean an automobile, and I wondered whether this was common usage for the time and place. I had not heard it before. To a modern reader, it has an archaic sound, as if the car were such a new development that there was not yet a specific word for it. But of course by the 1920s cars were very common, so this does not make sense. It may also be slang; given their criminal associations, Hammett's characters tend to speak mostly in slang.

Does anyone have more information about this usage and its history?