St. Pope Pius V was a Dominican. When the muslims were decimating the Catholics and the protestants revolting everywhere, he remembered his founder St. Dominic. When St. Dominic was discouraged with the conversion of the Albigensians, Our Lady appeared to him and explained that praying the Our Father and the Angelic Salutation “Hail Mary”, he would have success.
So St. Dominic began praying the Holy Rosary as Our Lady taught him while meditating on the Joyful, Sorrowful and Glorious events of Jesus’ life. He then had great success in his preaching and converting of the heretics and sinners.
For this reason, St. Pope Pius V asked all of Europe to pray the Holy Rosary for the success of the battle of Lepanto against the Muslim fleet. It is said that Our Lady appeared and frightened the muslims.
When St. Pope Pius V was in a meeting he was given a supernatural vision that the Battle had been won by Don Juan of Austria. He immediately turned to God and Our Lady in gratitude. A week later the news arrived that indeed the vision was correct.
Our Lady will not let us down. God listens to her.