Easter Rising in putting the rising off for only a day, although it greatly reduced the number of Volunteers who turned out. British Naval Intelligence had been aware of the arms shipment, Casement's return, and the Easter date for the rising through radio messages between Germany and its embassy in the United States that were intercepted by the Royal Navy and deciphered in Room 40 of the Admiralty. The information was passed to the Under-Secretary for Ireland, Sir Matthew Nathan, on 17 April, but without revealing its source, and Nathan was doubtful about its accuracy. When news reached Dublin of the capture
Easter Rising of the "Aud" and the arrest of Casement, Nathan conferred with the Lord Lieutenant, Lord Wimborne. Nathan proposed to raid Liberty Hall, headquarters of the Citizen Army, and Volunteer properties at Father Matthew Park and at Kimmage, but Wimborne insisted on wholesale arrests of the leaders. It was decided to postpone action until after Easter Monday, and in the meantime Nathan telegraphed the Chief Secretary, Augustine Birrell, in London seeking his approval. By the time Birrell cabled his reply authorising the action, at noon on Monday 24 April 1916, the Rising had already begun. On the morning of Easter Sunday,