対潜戦
By December 1941 operational requirements necessitated aircraft with an extra-long-range of 2,000 miles as U-boats were operating 700 miles from the British Isles. If patrols were deployed 350–600 miles covering port approaches, the enemy would move to the 600–700 mile area and out of range. By then ASV (air-to-surface-vessel) radar homing had been developed, and aircraft were being developed with all-weather and short-take off capabilities. Priority went to Coastal Command Anti-submarine warfare, units by this time. (Anti-submarine warfare was then denoted "A/S" but since been denoted "ASW")