An American declaration of war would not produce an instant Pacific fleet concentration. A Caribbean exercise and movement through the Panama Canal could delay major U.S. action until April or May 1939. That interval gives Britain time to fight Japan, accelerate construction, and prepare for a second opponent. German and Italian alignment also becomes a strategic variable because their decision changes the forces Britain can use in both oceans.
Chapter · 5:45-7:04
American intervention takes time while Germany and Italy choose sides
The scenario allows two or three months for the United States to mobilize and reposition its fleet, creating an opening in which Germany and Italy must decide whether to join Britain or remain neutral.