Traffic to the Mediterranean, Africa, and South America crossed an area used by German patrol aircraft and submarines. C-class cruisers supplied convoy air defense, while the persistent possibility of S-boat attack imposed alert and readiness costs even when no engagement occurred. New Dido-class ships bound for the Mediterranean could encounter their first concentrated land-based air attacks while crossing the Bay. This theater helps explain why Dido was designed to screen against air and light surface threats, whereas Atlanta emphasized destroyer-leader duties more strongly.
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Air and surface screening in the Bay of Biscay
The Bay of Biscay exposed cruisers and convoys to German aircraft, U-boats, and S-boats, making multi-threat screening more important than a narrow AA label suggests.