Eisenhower, as well as the officers and troops under him, had learned valuable lessons in their previous operations, and their skills had all strengthened in preparation for the next most difficult campaign against the Germans—a beach landing assault. His first struggles, however, were with Allied leaders and officers on matters vital to the success of the Normandy invasion; he argued with Roosevelt over an essential agreement with De Gaulle to use French resistance forces in covert and sabotage operations against the Germans in advance of Overlord. Admiral Ernest J. King fought with Eisenhower over King's refusal to provide additional landing craft from the Pacific. He also insisted that the British give him exclusive command over all strategic air forces to facilitate Overlord, to the point of threatening to resign unless Churchill relented, as he did. Eisenhower then designed a bombing plan in France in advance of Overlord and argued with Churchill over the latter's concern with civilian casualties; de Gaulle interjected that the casualties were justified in shedding the yoke of the Germans, and Eisenhower prevailed. He also had to skillfully manage to retain the services of the often unruly George S. Patton, by severely reprimanding him when Patton earlier had slapped a subordinate, and then when Patton gave a speech in which he made improper comments about postwar policy.