New evidence indicates the Allies urged His Holiness to be silent for fear of upsetting Russia.
The Catholic Herald's Simon Caldwell has the story, with my emphases:
US and British diplomats discussed exerting pressure on Pope Pius XII to be silent about the Nazi deportations of Hungarian Jews, according to newly discovered documentation.
The British feared that the wartime pope might make a “radio appeal on behalf of the Jews in Hungary” and that in the course of his broadcast would “also criticise what the Russians are doing in occupied territory”.
Sir Francis D’Arcy Osborne, the British ambassador to the Vatican, told an American diplomat that “something should be done to prevail upon the pope not to do this as it will have very serious political repercussions”.
Osborne’s comments were made to Franklin Gowen, an assistant to Myron Taylor, the US special representative to the Vatican.
Gowen recorded the conversation in a letter to Taylor, saying he had promised Osborne that he would bring his concerns to the “immediate attention” of the US ambassador.
“It was understood that, pending your reaction, he would not take any steps vis-a-vis the Holy See,” Gowen told Taylor.
In the letter, Gowen also said that Mgr Domenico Tardini, the Vatican assistant secretary of state, had told him 10 days earlier that Pope Pius would not “make any radio appeal because if he did so he would, in fairness, to all have to criticise the Russians”, a member of the Allies.
He said he withheld this information from Osborne in the belief that it would be best for Taylor to impart it himself following a meeting with Pope Pius scheduled the day after the letter was written.
The letter was dated November 7, 1944, as the Nazis were organising mass deportations of Jews from Budapest, the Hungarian capital, to death camps in Poland, Austria and Germany.
Rome had been liberated by the US Fifth Army the previous June and, with the Vatican behind Allied lines, the pope had more freedom to speak out.
But as the head of a neutral state, he understood that he could not condemn the war crimes of one side without condemning those of the other.
However, on November 19 – less than two weeks after Gowen wrote his letter – the Vatican joined the neutral states of Spain, Portugal, Switzerland and Sweden to appeal to the Hungarian government to end the deportations.
The British Jewish historian Sir Martin Gilbert, an internationally recognised expert on the Holocaust, said in his 2002 book, The Righteous: The Unsung Heroes of the Holocaust, that at that time the Catholic Church in Budapest was hiding 25,000 Jews in homes and religious institutions.
Simultaneously, the Red Army of the Soviet Union was advancing westward across Europe and killing and raping many innocent people as it was driving Adolf Hitler’s armies into retreat.
Gowen’s letter was made public for the first time by the New York-based Pave the Way Foundation, which is conducting research into the actions of Pope Pius, assisted by a US Catholic lawyer, Ronald Rychlak; German historian Michael Hesemann; and a journalist, Dimitri Cavalli.
Gary Krupp, president of the foundation, told the American Catholic News Service that the Allies feared any condemnation of Josef Stalin’s armies “would work against the unified war effort of the Allies”.
He said the letter was significant because it showed the pressures that confronted Pope Pius, who has been criticised for his alleged silence in the face of the Holocaust.
“The simple reality, which seems to be ignored by many critics, is that the Vatican was a neutral government that used its neutrality to save thousands of lives,” said Mr Krupp.
Gowen’s letter was found by Rychlak among Taylor’s documents and has been posted on the Pave the Way Foundation website.
Another letter made public by the foundation discusses help for Jewish fugitives, with Osborne telling Harold Tittman, another of Taylor’s aides, that it must be destroyed because it might endanger the life an Italian priest who was rescuing Jews if it fell into enemy hands.
It was dated May 20, 1944, barely three weeks before Rome fell to the Allies and, according to the Pave the Way Foundation, shows how the work of rescuing Jews was conducted in secrecy, with most documentary evidence of such activities destroyed almost instantly.