From When the Shooting Stopped: August 1945, by Barrett Tillman (Osprey, 2022), Kindle pp. 261-262:
With broad vision, two years before VJ Day, Army Chief of Staff George C. Marshall anticipated the need to return millions of servicemen to their homes. He raised the subject as early as 1943, and after D-Day in June 1944 some planners thought that VE Day might dawn by year’s end. But whenever the timeframe, some essential factors forced themselves upon joint staffs.
First was the need for large-capacity staging areas and processing facilities, not only in Europe but in the much broader expanse of the Pacific. Internal concerns within the U.S. included receiving ports and railroads capable of absorbing huge numbers of personnel and delivering them to “separation centers” in every state.
Paramount was shipping, as the vast majority of returnees had to travel by sea. The U.S. Navy was only marginally available at the time, with millions of tons of vessels committed to the two-phase invasion of Japan in November 1945 and March 1946. Therefore, heavy reliance was placed upon Army and Merchant Marine ships with some augmentation by Coast Guard vessels.
Tasked with finding enough hulls to meet the demand, the War Shipping Administration (WSA) came through. Shortly after VE Day it identified nearly 550 vessels capable of carrying useful numbers of personnel.
In the actual event, absent Operation Downfall, the Navy suddenly afforded a huge bonus for Operation Magic Carpet. Ten aircraft carriers, six battleships, and 26 cruisers were hastily modified to accept cheek-by-jowl accommodations for troops who willingly endured long days and nights at sea, returning to “Uncle Sugar.”
Within two months of Emperor Hirohito’s surrender announcement, more than 700 ships of all types were available, notably Liberty and Victory cargo ships. Foreign vessels obtained for the project included origins as diverse as Panama and Italy.
The record for returning troops home belonged to the veteran aircraft carrier Saratoga (CV-3), which embarked some 29,000 grateful veterans, as fleet carriers were among the fastest ships afloat. But for maximum capacity, living space was likened to cramming 12 pounds into a ten-pound bag. The new carrier Lake Champlain (CV-39), only commissioned in June, was altered to accept 3,300 bunks. On her first Magic Carpet mission she set a transatlantic record of 32 knots, only surpassed by the liner United States in 1952.
The millions of personnel returned from war zones were not limited to American servicemen. The Army and WSA allocated 29 troop ships to transport nearly 500,000 European war brides. On the other side of the globe, it was estimated that 12,000 Australian women married American servicemen as well.
Magic Carpet was an immense success. At the time of VE Day in May 1945 more than 3 million soldiers were stationed in Europe alone. By year’s end, seven months later, the Army counted fewer than 700,000 troops.
The Navy also experienced a huge reduction: from 3.3 million personnel in 1945 to fewer than 500,000 at the end of 1946.
Overall, Magic Carpet spanned the year following the climax in Tokyo Bay. On average, between September 1945 and September 1946 the operation landed 22,000 men and women at a U.S. port every day for 13 months. As noted by the National WWII Museum, “The sum total of which provides the mathematical framework behind the staggering post-war baby boom nine months later.”