Order affirmed. This petition for mandamus follows upon the sustaining by the Civil Service Commissioners of the disapproval by the respondent director of Civil Service of the petitioner’s alleged appointment as fire captain in the town of Marblehead. The trial judge dismissed the petition. In 1944 the town created five permanent positions in the fire department, a chief and four captains. The chief had given notice that he was retiring on March 31, 1962, and, upon receipt from the Department of Civil Service of a list of those eligible for promotion to the position of permanent captain, on March 28, 1962, he appointed the petitioner to the post of permanent captain, the appointment to be effective April 1, 1962. There was no vacancy in the position of fire captain when the chief attempted to make the appointment nor was there such a vacancy on April 1, 1962, by virtue of the chief’s retirement. A valid appointment required among other necessities an existing vacancy. See G. L. c. 31, § 20.