How did the Allied buildup in Britain prepare for the Normandy invasion?

The Allied buildup in Britain, which spanned two years, was a monumental logistical undertaking essential to the success of the Normandy invasion. This effort involved the trans-Atlantic shipment of 16 million tons of cargo to the British Isles, creating a vast administrative zone of depots, air bases, and supply parks.1

Key aspects of this preparation included:

• Strategic Air Campaign: Between April and June 1944, Allied air forces flew 200,000 sorties to isolate the invasion area by destroying bridges and transport networks, while simultaneously conducting deception operations to mislead the Germans regarding the invasion site.23
• Deception Operations: The Allies created a "phantom army" in southeast England to suggest an invasion of the Pas-de-Calais, supported by spurious radio transmissions and radar decoys.43
• Innovative Infrastructure: Recognizing that German defenses made capturing existing ports difficult, the British engineered Mulberry artificial harbors. These portable ports were fabricated in secrecy and towed across the English Channel to facilitate the rapid off-loading of vehicles and supplies.5
• Unified Command: The Supreme Headquarters Allied Expeditionary Force (SHAEF) integrated the land, sea, and air forces of the Allied nations, ensuring a coordinated logistical and operational effort.6