German invasion of the Netherlands
One of them was Colonel Hans Oster, a German intelligence officer. In March 1939 he began to pass information to his friend, a Dutch military officer in Berlin Major Gijsbertus J. Sas. This information included the German attack date.  Sas informed the Allies. Sas knowing the date of the attack on Denmark and Norway was not noticed. Though he said a German armoured division would try to attack the Netherlands and that there was a plan to capture the Queen, the Dutch defence plan was not changed.