Since the 18th century, all workers in the maritime sector (sailors, fishermen, shipwrights, and dock workers) were required to perform their military service in the navy. To organize and control all this, the Matrícula de Mar was instituted, and after 1874 this was replaced by the Inscripción Marítima. In each maritime district there was an official registry in charge of the marine authorities in which all these men were registered, this was the Libro de Registro de Matriculados or Inscritos Marítimos. In these registers there was an individual entry for each member of the register, which could be unequivocally identified by their registration number. The registry included his full name, place and date of birth, the names of the father and mother, the place of residence, and the dates of incorporation into the registration, among other elements.