Navajas are traditional Spanish folding knives. They were popular with sailors of the Spanish Main who regularly carried them in their waistbands. Sixteen Navaja-style knives were recovered from the wrecks of the Nuestra Senora de Atocha and Santa Margarita. Both galleons sank in 1622. (1)
Though best known for fighting and personal defense, Navajas were used for everything from cutting lines, peeling fruit to shaving. They were even used to preform surgery. (2)
Over time a locking style blade with a backspring evolved. These knives were called Navaja de Muelles (Spring Knifes). A metal pull ring to release the lock was added in the late 18th century. The ring was eventually discarded in favor of a lever.