Section 59. The words “retiring authority”, as used in sections fifty-six to sixty, inclusive, shall mean as to the commonwealth, the state board of retirement; as to a county, city, town, district or regional school district, the appropriate retirement board established under section twenty, having jurisdiction in the governmental unit in which a veteran was employed at the time of his retirement or death, or, if there is no such board in the case of a town, the selectmen; or, in the case of a district, the prudential committee; or, in the case of a regional school district, the regional district school committee; or, in the case of a housing authority, the housing authority; or in the case of any redevelopment authority, the redevelopment authority.