Pope Pius XII on the diaconate

Just came across this quote this morning:

We have not yet considered those Orders which precede the priesthood, and which, in the present practice of the Church, are only conferred in preparation for ordination to the priesthood. The duties connected with Minor Orders have long been performed by laymen, and We know that thought is being given at present to the introduction of a diaconate conceived as an ecclesiastical office independent of the priesthood. Today, at least, the idea is not yet ready for application. Should it someday become so, what We have just said would still hold true and this diaconate would take its place with the priesthood in the distinctions We have just drawn. (Pope Pius XII, October 5, 1957, Guiding Principles of the Lay Apostolate 1)

Sure enough, over the next 15 years, conditions became favorable. In 1964, the Second Vatican Council said the following:

At a lower level of the hierarchy are deacons, upon whom hands are imposed "not unto the priesthood, but unto a ministry of service." ... [T]he diaconate can in the future be restored as a proper and permanent rank of the hierarchy. It pertains to the competent territorial bodies of bishops, of one kind or another, with the approval of the Supreme Pontiff, to decide whether and where it is opportune for such deacons to be established for the care of souls. With the consent of the Roman Pontiff, this diaconate can, in the future, be conferred upon men of more mature age, even upon those living in the married state. It may also be conferred upon suitable young men, for whom the law of celibacy must remain intact. (Lumen Gentium 29)

In 1967 (a mere decade after Pope Pius XII's statement), Pope Paul VI promulgated an Apostolic Letter motu proprio, Sacrum Diaconatus Ordinem, restoring the permanent diaconate to the Church.  (It's not a very long document, and I'd recommend it for anyone interested in knowing about the vocation and duties of the permanent diaconate.)

Then, five years later, Pope Paul VI promulgated another Apostolic Letter Ad Pascendum, containing further norms for the permanent diaconate.  (This too is a short document and recommended reading.)