From the state archives: "Like ships of the sea, the giant clippers of Pan American World Airways, too, must come in for a "dry docking." And this requires special equipment, particularly in the case of the double-deck 'strato' clippers; largest commercial airliners in operation. To handle the huge planes, Pan Am designed and built a special dock, consisting of movable and stationary sections, which provides quick access to all parts of the giant clipper. The dock weighs 75 tons."
The state archive says 1940 for the date but these aircraft didn't start being delivered to Pan American until 1949.
The Boeing 377 had 86 seats, a lower deck lounge and cocktail bar, a 2750 mile range, four Pratt & Whitney R-4360 engines (3500hp) and was the last of the Pan American Clippers to carry radio operators in the cockpit. It could fly at 340 mph, had a 142,500 lb. max gross takeoff weight, was 110 feet in length, 38 feet high and had a 141 foot wingspan. A fleet of 20 B377s were ordered by Pan Am on November 28, 1945, and the first one was put into service on April 1, 1949 on the San Francisco to Honolulu route. Pan American obtained eight more B377s from a merger with American Overseas Airways.