thanks.
My brother did a report for a caribbean sociology class on the Jamaican gangs in the 60s, and several of his sources say that they were german switchblades. Michael Thelwell's book "the harder they come" gives an excellent description of the life of Trenchtown denizens and describes the rachet as an okapi, with its "wicked humpbacked blade".
the ratcheting sound of the knife opening, however, was used in intimidation, as well as the speed with which the user opened his knife, and the technique they used to open it.
I've had okapis and they do ratchet but I've never been able to open one quickly.
thanks for the info, I hadn't thought of the navaja before
peter