Pope Paul VI
On basic Church teachings, the pope was unwavering. On the tenth anniversary of Humanae vitae, he reconfirmed this teaching. In his style and methodology, he was a disciple of Pius XII, whom he deeply revered. He suffered for the attacks on Pius XII for his alleged silences during the Holocaust. Pope Paul VI was less outstanding than his predecessors: he was not credited with an encyclopedic memory, nor a gift for languages, nor the brilliant writing style of Pius XII, nor did he have the charisma and outpouring love, sense of humor and human warmth of John XXIII. He took on himself the unfinished reform work of these two popes, bringing them diligently with great humility and common sense and without much fanfare to conclusion. In doing so, Paul VI saw himself following in the footsteps of the Apostle Paul, torn to several directions as Saint Paul, who said, "I am attracted to two sides at once, because the Cross always divides."
On which anniversary of his Humanae Vitae did Paul VI reconfirm the beliefs set forth by the Humanae Vitae? 
tenth
On the tenth anniversary of Humanae vitae, he reconfirmed this teaching.
Paul VI