From the War Cabinet minutes of 4th September 1939:
6. The First Lord of the Admiralty reported that steamship Athenia outward bound with 300 Americans on board had been sunk 200 miles north-west of Ireland at 2 PM on 3 September, 1939. It was understood that the passengers and crew were in the ship’s boats. Two destroyers were hastening to the rescue and should be near the scene. The occurrence should have a helpful effect as regards public opinion in the United States.
The steamship Blairbeg had been sunk 70 miles north west of Ireland. H. M. S. Renown had detached her anti-submarine escort of two destroyers to the rescue.
The War Cabinet were informed that the routing of merchant ships was in force, but the convoy system had not yet started. Reference was made to the statement in the joint Anglo-French declaration that we should abide by the Submarine Protocol of 1936. Germany was one of the powers which had adhered to the protocol.
7. The Chief of the Imperial General Staff reported on the position as regards the air defences of Great Britain and the date of arrival in France of the Field Force. The Chief of the Imperial Gen staff gave the War Cabinet is a picture of the military situation in Poland as he saw it. The concentration of as many as 32 divisions in Slovakia had come as a surprise. The country between Slovakia and Poland was extremely difficult for military operations, and presented administrative problems of great magnitude. If the Germans were able to carry out their plan, the Poles would have to face an attack in enormous strength from the south.
The Chief of the Imperial General Staff expressed a personal view that the crushing of Poland by Germany in a few weeks with most improbable.