law: 16. Calling up for service.-
  The competent authority may cause to be served on any person whose name is entered in the register maintained in pursuance of section 15 a written notice stating that he is called up for service in the Air Defence Reserve and requiring him to present himself at such place and time and to such authority as may be specified in the notice; and the person upon whom the notice is served shall be deemed to be enrolled in the Reserve as from the day so specified.