Combination pocket knife/"revolver"

 Images Uploads Knife Gun Thumb

From a 1930s Johnson Smith & Co catalog, "The Defender," a combo pocket knife/"revolver." It's clearly "a most useful combination that will be thoroughly appreciated by sportsmen, hunters, campers, night watchmen, cyclists, automobilists, travellers, ladies, and the public generally… Nothing could be more serviceable on a fishing tramp as it obviates the necessity of carrying a heavy gun." (via Weird Universe)