General Roman Calendar of 1960
On 25 July 1960, Pope John XXIII approved a revision to the General Roman Calendar by his motu proprio, Rubricarum instructum. It was promulgated by the Sacred Congregation of Rites the following day, 26 July 1960, by the decree Novum rubricarum.
Source: Wikipedia — General Roman Calendar of 1960 (CC BY-SA 4.0)