The following article from The Latin Mass Magazine was written by Mr. Davies and its relevence to Summorum cannot be understated. You can read the whole article HERE. The following in an excerpt:
The liturgical destruction did not begin in 1969 with the promulgation of the new rite of Mass, the Novus Ordo Missae. The debacle was well under way in 1965 when the Vatican allowed its liturgical bureaucrats to begin revising the Missal that had last been revised in 1962. The 1962 Missal incorporated the mainly rubrical changes contained in the General Decree Novum Rubricarum of the Sacred Congregation of Rites of July 26, 1960. This rubrical reform had been ordered by Pope Pius XII, and few of the changes would have been noticed by the layman using a pre-1962 Missal apart from the omission of the second Confiteor before the Communion of the Faithful. In pre-1962 Missals in the Ritus servandus in celebratione Missae, X, 6, this Confiteor is stipulated. In the same section in the 1962 Missal it is not mentioned, but nowhere in the rubrics is it forbidden. Apart from this omission the ordinary of the Mass was not changed.
No layman could help noticing the changes made to the Ordinary of the Mass in the 1965 Missal, and there can be little doubt that its purpose was to prepare the faithful for the revolutionary changes that were to be introduced in 1969. By design or by coincidence the preparation for this revolution followed precisely the strategy of Thomas Cranmer, the apostate Archbishop of Canterbury, prior to the imposition of his English Communion Service of 1549. One of the principal features of the Catholic liturgy had been stability. Developments in the manner in which Mass was celebrated did occur, but they crept in almost imperceptibly over the centuries, and the Missals in use in England and throughout Europe in the sixteenth century had remained unchanged for at least several hundred years. The faithful took it for granted that whatever else might change, the Mass could not. In order to avoid provoking resistance among the Catholic faithful Cranmer deemed it prudent not to do too much too soon. Parts of the Mass were celebrated in the vernacular – but, many insisted, it was still the same Mass, so why risk persecution by protesting? New material was introduced into the unchanged Mass, which while open to a Protestant interpretation was in no way specifically heretical; once again, why protest?
An important innovation was the imposition of Communion under both kinds for the laity at the end of 1547. Catholics in England made the mistake of conceding this change without opposition for the sake of peace. The great Catholic historian Cardinal Francis Gasquet writes:
It was, after all, only a matter of ecclesiastical discipline, although some innovators in urging the incompleteness of the Sacrament, when administered under one kind, gave a doctrinal turn to the question which issued in heresy. The great advantage secured to the innovators by the adoption of Communion under both kinds in England was the opportunity it afforded them of effecting a break with the ancient missal.