sleeve daggers and lapel daggers got their start from the OSS behind the front lines covert operatives in world war two. The sleeve dagger is a longer version of the lapel or thumb dagger, these knives were often used with a laynard that served as a flexible handle and also anchored the blade to the hand for a thrust. Fred Perrin bases alot of his blades on this type of concealed fighting knife. These daggers were not always double edged. For a great web site where you can see different examples and read more about this try Don Rearic's homepage. look at covert knives. Illegal, yes ofcourse completely and without question illegal.