Though Pius acted discreetly, he did not hide Hitler's attack plan under the proverbial bushel basket. During the second week of January 1940, a general fear gripped Western diplomats in rome as the pope's aides warned them of the German offensive, which Hitler had just rescheduled for the 14th. On the 10th, a Vatican prelate warned the Belgian ambassador at the Holy See, Adrien Nieuwenhuys, that the Germans would soon attack in the West. ...This isn't making great bedtime reading because it is complex enough to require more attention than I can give in a sleepy state. However, it is endlessly fascinating watching the interwoven strands of this previously unknown story of attempts to stop Hitler.
Pius had in fact already shared the warning, while shielding the source. On 9 January, Cardinal Maglione directed the papal agent in Brussels, Monsignor Clemente Micara, to warn the Belgians about a coming German attack. Six days later, Maglione sent a similar message to his agent in The Hague, Monsignor Paolo Giobbe, asking him to warn the Dutch.
That same month, Pius made a veiled feint toward public protest. He wrote new details on Polish atrocities into Radio Vatican bulletins. But when Polish clergy protested that the broadcasts worsened the persecutions, Pius recommitted to public silence and secret action.
Mark Riebling, Church of Spies