Pope John XXIII issues the Apostolic Constitution, Humanae salutis, formally calling for the Second Vatican Ecumenical Council which will start next year. In it, he specifically singles out "militant atheism" as one of his primary concerns about the modern world.
Pope John XXIII writes at the beginning, under the headline Painful Considerations:
"Today the Church is witnessing a crisis underway within society. While humanity is at the threshold of a new age, immensely serious and broad tasks await the Church, as in the most tragic periods of her history.
It is a question in fact of bringing the perennial life-giving energies of the Gospel to the modern world, a world that boasts of its technical and scientific conquests but also bears the effects of a temporal order that some have wanted to reorganize by excluding God.
This is why modern society is characterized by great material progress but without a corresponding advance in the moral sphere.
Thence a weakening in aspirations towards the values of the spirit; thence the tendency to seek only the earthly pleasures that technological progress brings so easily within the reach of all; thence also a quite new and disturbing fact: the existence of a militant atheism operating all over the world."