On August 13, Chain Home radar detected an unusually large German approach: multiple formations of bombers and fighters crossing from Normandy. RAF sector commanders responded by sending more than one hundred fighters into the air and guiding them by radar and ground reports. The resulting battles were the fiercest yet, with German bombs falling on Southampton and other places across southern England, but not on London, which left British observers uncertain about the attackers' real objective.

Because the bombing seemed scattered across airfields, harbors, ships, and towns, British officials found the raids perplexing rather than clearly strategic. Initial RAF claims said seventy-eight German bombers had been destroyed for the loss of only three British pilots, producing jubilation in Downing Street, but the true totals were lower: forty-five Luftwaffe aircraft lost against thirteen RAF planes. Even so, the day marked the opening of Germany's major air offensive against Britain, though those living through it did not yet fully understand that they were at the start of what would later be called the Battle of Britain.

In Washington the same day, Franklin Roosevelt decided to transfer fifty old destroyers to Britain by executive action instead of seeking congressional approval first. Roosevelt informed Winston Churchill, who was pleased by the breakthrough but immediately worried about the political cost at home. Churchill feared that if the arrangement looked like Britain was trading sovereign territories for obsolete ships, Parliament and the public would resent it, so he urged Roosevelt to present the destroyers and the base leases as separate acts of mutual aid rather than a blunt bargain.

Roosevelt, however, had his own political constraints. With neutrality laws and the heated debate over conscription already shaping the American election, Roosevelt needed Americans to see the deal as both legally defensible and beneficial to United States security, not as a simple gift to Britain. Churchill later recognized that the destroyer transfer was so un-neutral that, by traditional standards, Germany could have treated it as grounds for war against the United States.

On August 14, Göring's planned second day of intensified attacks was again weakened by poor weather, which grounded many German aircraft. Some raids still went forward, including a mission escorted by Adolf Galland, who welcomed the chance to fight over the Strait of Dover where fuel limits would give him more combat time. Guided by radar, RAF squadrons intercepted the force; Galland first missed one Hurricane, then anticipated another pilot's exit from cloud cover and shot that aircraft down. Even on this reduced day, the Luftwaffe lost nineteen aircraft to the RAF's eight, leaving Göring deeply dissatisfied.