Following Germany’s Blitzkrieg attack and conquest of Poland in 1939, there was an unexpected period of stalemate in western Europe with little fighting and no major conflicts. Britain, however, was expecting a major German air attack so civil defence plans were enforced, including conscription, food rationing and blackout, along with the introduction of the Emergency Powers (Defence) Bill. The Royal Navy was well aware of the threat posed by German U-boats to trans-Atlantic shipping. In 1939, great reliance was placed on ASDIC sonar, and the sinking of the pocket battleship Graf Spree in December 1939 was a boost to morale. It was becoming increasingly clear, however, that convoys with naval escorts would need to be provided to protect shipping from submarine attacks on long journeys across the Atlantic Ocean. The Phoney War came to an end in April 1940 when Nazi forces attacked Scandinavia.
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