Pope Pius XII made the decree 23 March 1955,Acta Apostolicae Sedis 47(1955), pages 218-224 enacting several changes to the General Roman Calendar, which had been most recently updated in 1954. That version remained in force until 1960, when Pope John XXIII decreed a new revision, called the General Roman Calendar of 1960.
The General Calendar of Pope Pius XII is not authorized for liturgical use by traditional groups in communion with the Holy See. Most sedevacantists prefer to use the General Roman Calendar of 1954,Pre-Vatican II Liturgical Changes : Road to the New Mass by Most Rev. Daniel L. Dolan, The Roman Catholic, June 1983Liturgical Revolution by Rev. Francesco Ricossa, The Roman Catholic, February–April 1987Is Rejecting the Pius XII Liturgical Reforms Illegal? by Rev. Anthony Cekada, 27 April 2006More on the Legal Issue by Rev. Anthony Cekada, 10 July 2006 as well as Old Roman Catholics, as their members consider it to be the last calendar before by the revisions that began in 1955. However, a few sedevacantists do observe the revisions beginning in 1955, while excluding those of the John XXIII, such as the Congregation of Mary Immaculate Queen.The Liturgical Changes of Pope Pius XII : May a Catholic Reject Laws Promulgated by a Legitimate Pope?, by Rev. Fr. Dominic Radecki, The Reign of Mary, Issue No. 161Statement of Principle : CMRI and the Liturgy of Pope Pius XII (including the revised Holy Week), Mount Saint MichaelSacred Heart of Jesus ChurchChapel of the Most Holy Trinity
Changes to the Calendar
Rank of feasts The grade and rite of "Semi-Double" was suppressed, and the liturgical days formerly celebrated as that rite were to be celebrated in the simple rite except the Vigil of Pentecost which was raised to the double rite.Title II: Changes in the calendar, 1-2
Sundays The Sundays of Advent and Lent and those that follow up to Low Sunday, and also Pentecost Sunday, were to be celebrated as doubles of the first class, outranking all feasts; but when feasts of the first class occurred on the second, third or fourth Sunday of Advent, Masses of the feast were permitted except the conventual Mass. Sundays previously celebrated in the Semi-Double rite were raised to the Double rite. An impeded Sunday Office and Mass was to be neither anticipated nor resumed. A feast or title or any mystery of Jesus falling on a Sunday per annum was thenceforth to take the place of the Sunday, with the latter merely commemorated.Title II: Changes in the calendar, 3-7
Vigils The Vigil of the Nativity of the Lord and the vigil of Pentecost were privileged vigils. The Vigils of the Ascension of Our Lord, the Assumption of the Blessed Virgin Mary, Saint John the Baptist, Saints Peter and Paul and Saint Lawrence were to be common vigils and, if they occurred on a Sunday, were not to be anticipated, but simply omitted. All other vigils, including those marked in particular calendars, were suppressed.Title II: Changes in the calendar, 8-10
Octaves Only the Octaves of Easter, Christmas and Pentecost were to be celebrated; all others occurring either in the universal or in particular calendars were suppressed. The days within the Easter and Pentecost octaves were raised to the Double rite, had precedence over all feasts, and did not admit commemorations. But the days in the Octave of Christmas, although of the Double rite, continued to be celebrated as before.Title II: Changes in the calendar, 11-13
From 2 to 5 January, unless some feast occurred, the Office was to be of the current feria in the simple rite. The Mass was to be the same as that of 1 January but without the Credo and the special "Communicantes".Title II: Changes in the calendar, 14
With the suppression of the Octave of Epiphany, the days from 7 to 12 January became feriæ per annum (in the Simple rite); up to the Sunday following Epiphany, the Mass was to be the same as that of the Epiphany, but without the Credo and without the special "Communicantes"; after the Sunday, the mass was to be that of the Sunday (which on that Sunday itself remained continually impeded by the Feast of the Holy Family). On 13 January the Commemoration of the Baptism of our Lord was to be celebrated in the major double rite, using for the Office and the Mass those previously said on the Octave of the Epiphany. But if 13 January occurred on Sunday, the Office and Mass were to be those of the "Feast of the Holy Family" without any commemoration of the Baptism of Our Lord.Title II: Changes in the calendar, 15-16
The days from the Ascension of Our Lord to the Vigil of Pentecost exclusive became feriæ of Eastertide (in the Simple rite); the Mass was to be that of the Feast of the Ascension, but without the Credo and the special Communicantes (even on the Friday before Pentecost, where hitherto the Mass of the Sunday had to be taken). The days of the suppressed Octaves of Corpus Christi and the Most Sacred Heart of Jesus became feriæ per annum.Title II: Changes in the calendar, 17-19
Feasts of the Saints Saints' feasts previously celebrated in the Semi-Double rite were to be treated as Simple feasts, and those previously celebrated in the Simple rite were reduced to a commemoration. If any feast not of the first or second class occurred on the ferias of Lent and Passiontide, from Ash Wednesday to the Saturday before Palm Sunday, the Office (if recited privately) and the Mass could be either of the feria or of the feast.Title II: Changes in the calendar, 20-22
Changes related to St. Joseph and others By a separate decree of the same year 1955, Pope Pius XII instituted the feast of "Saint Joseph the Worker" on 1 May (moving the feast of "Saints Philip and James Apostles" from 1 May, where it had been since the sixth century, to 11 May, and suppressing the "Solemnity of Saint Joseph, Spouse of the Blessed Virgin Mary" that, since Pope Pius IX's decree of 10 September 1847, had been celebrated on the second Wednesday after the Octave of Easter).Acta Apostolicae Sedis 47(1955), page 406
January 1: Circumcision of the Lord and Octave of the Nativity, Double of the II Class. 2: Feria 3: Feria 4: Feria 5: Com. of St. Telesphorus Pope and Martyr. 6: Epiphany of the Lord, Double of the I Class. 7: Feria 8: Feria 9: Feria 10: Feria 11: Com. of St. Hyginus Pope and Martyr. 12: Feria 13: Baptism of our Lord Jesus Christ, Greater Double. 14: St. Hilary Bishop, Confessor, and Doctor of the Church, Double, Com. of St. Felix Priest and Martyr. 15: St. Paul first hermit, Confessor, Double, Com. of St. Maurus. 16: St. Marcellus I Pope and Martyr, Simple. 17: St. Anthony Abbot, Double. 18: Chair of St. Peter Apostle at Rome, Greater Double, Com. of St. Paul Apostle, and of St. Prisca Virgin and Martyr. 19: Com. of Ss. Marius, Martha, Audifax, and Abachum Martyrs, Com. of St. Canute, Martyr. 20: Ss. Fabian Pope and Sebastian Martyrs, Double. 21: St. Agnes, Roman Virgin and Martyr, Double 22: Ss. Vincent and Anastasius Martyrs, Simple. 23: St. Raymund of Peñafort Confessor, Simple, Com. of St. Emerentiana Virgin and Martyr. 24: St. Timothy Bishop and Martyr, Double. 25: Conversion of St. Paul Apostle, Greater Double, Com. of St. Peter. 26: St. Polycarp Bishop and Martyr, Double. 27: St. John Chrysostom Bishop, Confessor, and Doctor of the Church, Double. 28: St. Peter Nolasco Confessor, Double, Com. of St. Agnes Virgin and Martyr second. 29: St. Francis de Sales Bishop, Confessor, and Doctor of the Church, Double. 30: St. Martina Virgin and Martyr, Simple. 31: St. John Bosco Confessor, Double.
Sunday between the Circumcision and Epiphany [or January 2, when no such Sunday occurs]: The most holy Name of Jesus, Double of the II Class. Sunday after Epiphany: The Most Holy Family of Jesus, Mary, Joseph, Greater Double.
February 1: St. Ignatius Bishop and Martyr, Double. 2: Purification of the Blessed Virgin Mary, Double of the II Class. 3: Com. of St. Blase Bishop and Martyr. 4: St. Andrew Corsini Bishop and Confessor, Double. 5: St. Agatha Virgin Martyr, Double. 6: St. Titus Bishop and Confessor, Double, Com. of St. Dorothy Virgin Martyr. 7: St. Romuald Abbot, Double. 8: St. John of Matha Confessor, Double. 9: St. Cyril Bishop of Alexandria, Confessor, and Doctor of the Church, Double, Com. of St. Apollonia Virgin Martyr. 10: St. Scholastica Virgin, Double. 11: Apparition of the Blessed Virgin Mary Immaculate, Greater Double. 12: The Seven Holy Founders of the Order of Servants of the Blessed Virgin Mary Confessors, Double. 13: Feria 14: Com. of St. Valentine Priest and Martyr. 15: Com. of Ss. Faustinus and Jovita Martyrs. 16: Feria 17: Feria 18: Com. of St. Simeon Bishop and Martyr. 19: Feria 20: Feria 21: Feria 22: Chair of St. Peter at Antioch, Greater Double, Com. of St. Paul. 23: St. Peter Damian Confessor, Double. 24: St. Matthias Apostle, Double of the II Class. 25: Feria 26: Feria 27: St. Gabriel of Our Lady of Sorrows, Double 28: Feria
In leap year the month of February is of 29 days, and the Feast of St. Matthias is celebrated on the 25th day and the Feast of St. Gabriel of Our Lady of Sorrows on the 28th day of February, and twice is said Sexto Kalendas, that is on the 24th day and 25th day; and the dominical letter, which was taken up in the month of January, is changed to the preceding; that, if in January, the dominical letter was A, it is changed to the preceding, which is g, etc.; and the letter f is kept twice, on the 24th and 25th.Kalendarium, Breviarium Romanum: "In anno bissextili mensis Februarius est dierum 29, et Festum S. Matthiæ celebratur die 25 ac Festum S. Gabrielis a Virgine Perdolente die 28 Febr., et bis dicitur Sexto Kalendas, id est die 24 et die 25; et littera dominicalis, quæ assumpta fuit in mense Januario, mutatur in præcedentem; ut, si in Januario, littera dominicalis fuerit A, mutetur in præcedentem, quæ est g, etc.; et littera f bis servit, 24 et 25.
March 1: Feria 2: Feria 3: Feria 4: St. Casimir Confessor, Simple, Com. of St. Lucius I Pope and Martyr. 5: Feria 6: Ss. Perpetua and Felicity Martyrs, Double. 7: St. Thomas Aquinas Confessor and Doctor of the Church, Double. 8: St. John of God Confessor, Double. 9: St. Frances of Rome Widow, Double. 10: The Forty Holy Martyrs, Simple. 11: Feria 12: St. Gregory I Pope, Confessor, and Doctor of the Church, Double. 13: Feria 14: Feria 15: Feria 16: Feria 17: St. Patrick Bishop and Confessor, Double. 18: St. Cyril Bishop of Jerusalem, Confessor, and Doctor of the Church, Double. 19: St. Joseph, Spouse of the Blessed Virgin Mary, Confessor, and Patron of the Universal Church, Double of the I Class. 20: Feria 21: St. Benedict Abbot, Greater Double. 22: Feria 23: Feria 24: St. Gabriel the Archangel, Greater Double. 25: Annunciation of the Blessed Virgin Mary, Double of the I Class. 26: Feria 27: St. John Damascene Confessor and Doctor of the Church, Double. 28: St. John Capistran Confessor, Simple. 29: Feria 30: Feria 31: Feria
Friday after Passion Sunday: Seven Sorrows of the Blessed Virgin Mary, Greater Double, Com. of the Feria.
April 1: Feria 2: St. Francis of Paula Confessor, Double. 3: Feria 4: St. Isidore Bishop, Confessor, and Doctor of the Church, Double. 5: St. Vincent Ferrer Confessor, Double. 6: Feria 7: Feria 8: Feria 9: Feria 10: Feria 11: St. Leo I Pope, Confessor, and Doctor of the Church, Double. 12: Feria 13: St. Hermenegild Martyr, Simple. 14: St. Justin Martyr, Double, Com. of Saints Tiburtius, Valerian and Maximus, Martyrs. 15: Feria 16: Feria 17: Com. of St. Anicetus Pope and Martyr. 18: Feria 19: Feria 20: Feria 21: St. Anselm Bishop, Confessor, and Doctor of the Church, Double. 22: Ss. Soter and Cajus Popes and Martyrs, Simple. 23: St. George Martyr, Simple. 24: St. Fidelis of Sigmaringen Martyr, Double. 25: St. Mark Evangelist, Double of the II Class. 26: Ss. Cletus and Marcellinus Popes and Martyrs, Simple. 27: St. Peter Canisius Confessor and Doctor of the Church, Double. 28: St. Paul of the Cross Confessor, Double, Com. of St. Vitalis Martyr.