I’m preparing to begin my document-by-document analysis of the conciliar texts, which will proceed in order of promulgation (and in alphabetical order for documents promulgated on the same date). That means Sacrosanctum Concilium, the Council’s constitution on the liturgy, will come second, after a brief treatment of Inter Mirifica.
In the meantime, Fr. Hunwicke has an excellent post up today pushing a line not heard often enough: officially-sanctioned liturgical reform fever began, not with Paul VI or John XXIII, but with Pius XII.
It was Pope Pius who kicked off the reformist frenzy in the Church, first by giving the modernist exegetes at the Biblicum free reign to deface the Psalter of the Roman Breviary (they promptly imposed an artificial pseudo-Ciceronian translation in place of St. Jerome’s Latin Vulgate, which had enjoyed use since ancient times) and then by embarking on a deeply reductionist reform of the liturgies of Holy Week, which Evelyn Waugh complained had badly impoverished the Church:
During the last few years we have experienced the triumph of the liturgists’ in the new arrangement of the services for the end of Holy Week and for Easter. For centuries these had been enriched by devotions which were dear to the laity—the anticipation of the morning office of Tenebrae, the vigil at the Altar of Repose, the Mass of the Presanctified. It was not how the Christians of the second century observed the season. It was the organic growth of the needs of the people. Not all Catholics were able to avail themselves of the services but hundreds did, going to live in or near the monastic houses and making an annual retreat which began with Tenebrae on Wednesday afternoon and ended at about midday on Saturday with the anticipated Easter Mass. During those three days time was conveniently apportioned between the rites of the church and the discourses of the priest taking the retreat, with little temptation to distraction. Now nothing happens before Thursday evening. All Friday morning is empty. There is an hour or so in church on Friday afternoon. All Saturday is quite blank until late at night. The Easter Mass is sung at midnight to a weary congregation who are constrained to ‘renew their baptismal vows’ in the vernacular and later repair to bed. The significance of Easter as a feast of dawn is quite lost, as is the unique character of Christmas as the Holy Night. I have noticed in the monastery I frequent a marked falling-off in the number of retreatants since the innovations or, as the liturgists would prefer to call them, the restorations. It may well be that these services are nearer to the practice of primitive Christianity, but the Church rejoices in the development of dogma; why does it not also admit the development of liturgy? 
Writer Nino Badano called the re-translation of the Psalter a “profanation” and suggested it was borne of Pope Pius’ “obsession with a formalistic perfectionism” and a certain “scruple of philological precision.”  And Fr. Stefano Carusi, I.B.P., writing recently on the Holy Week reforms, points out that the “entire raison d’être of the reform seems to be permeated with the whiff of rationalism and archeologism, with at times dollops of pure imagination”  — rather like the reforms imposed on the Church in the 1965-1970 period.
Finally, we might do well to remember that the major actors of the Council were, so far as I can tell, to a man elevated to the episcopate or even the Cardinalate by Pius XII over the course of his long reign — Annibale Bugnini was his liturgical point-man; Augustine Bea, his personal confessor; Montini (the future Paul VI) was his Secretary of State; and he elevated both Roncalli (John XXIII) and conciliar archvillain Josef Frings to the Cardinalate.
The groundwater was tainted long before 1958.
 Evelyn Waugh, “The Same Again, Please.” The Spectator, 23 November 1962. [Link]
 Nino Badano, I primi giorni della Chiesa e gli ultimi (Rome: Volpe, 1973), 158-159. Qtd. in Roberto de Mattei, The Second Vatican Council: An Unwritten Story, Trans. Patrick T. Brannan, S.J., Michael J. Miller, and Kenneth D. Whitehead (Fitzwilliam, NH: 2010), 31-32.
 Fr. Stefano Carusi, “The Reform of the Holy Week in the Years 1951-1956.” Originally published on Disputationes Theologicae, 28 March 2010 [Link]; English translation by Fr. Charles W. Johnson republished on Rorate Caeli, 25 July 2010 [Link].