As they prepared for a cross-Channel assault on France, the Western Allies built up on British soil one of the largest and most powerful invasion forces in history. For 2 months before the landing, while troops, equipment, and supplies poured into Britain, the Allied air forces bombed railroads, bridges, airfields, and fortifications in France and Belgium and continued their attacks on German industrial centers. Postponed by delays in gathering the necessary landing equipment and by weather and tidal conditions, Operation Overlord, with Eisenhower in command, began on June 6, 1944, afterward known as D-Day. Throug