Invincible ignorance and protestants - magisterium

Q. 168. Can they be saved who remain outside the Catholic Church because they do not know it is the true Church?

A. They who remain outside the Catholic Church through no grave fault of their own and do not know it is the true Church, can be saved by making use of the graces which God gives them.

• Those who are outside the Church through no fault of their own are not culpable in the sight of God because of their invincible ignorance. Persons who make use of the graces God gives them, even though they are not members of the true Church, actually have the desire to become members inasmuch as they wish to use all the means ordained by God for their salvation.

• We should pray and try to persuade others to investigate the teachings of the Catholic Church because charity obliges us to do all we can to lead others to salvation. We should also pray for Catholic missioners and help them in their work of bringing the faith to those outside the Catholic Church.

Baltimore Catechism 3, Lesson 12, Q168

This is the revised Catechism from the 40's I believe

Membership of the Church is necessary for all men for salvation [De fide]

In the Creed Caput Firmiter, the Fourth Lateran Council (1215) declared: "There is indeed one universal Church of the faithful outside of which no one at all is saved" (extra quam nullus omnino salvatur). This was also the teaching of the Union Council of Florence, and of the Popes Innocent III, Pope Boniface VIII in the Bull Unam sanctam, Clement VI, Benedict XIV, Piux IX, Leo XIII, and Pius XII in the Encyclical Mystici Corporis. As against modern religious indifferentism, PIus IX declared: "By Faith it is to be firmly held that outside the Apostolic Roman Church none can achieve salvation. This is the only ark of salvation. He who does not enter into it, will perish in the flood. Nevertheless it is to be held as equally certain that those who suffer from ignorance of the true religion, if this ignorance should be invincible, are not subject to blame in this matter before the eyes of the Lord." The last proposition holds out the possibility that people who in fact (actu) do not belong to the Church can achieve salvation.

From Ott's Fundamentals of Catholic Dogma (Internal citations to Denzinger omitted).