Conditions in the United States changed dramatically on December 7, 1941: the Japanese attacked Pearl Harbor, resulting in enormous losses in US lives and warships. The US Congress declared war, and the subtle preparations that had been evident to a careful observer for some time suddenly became overt and intense.

Everyone's life would be affected by the events that followed, and they would have a share in the burden of the war that had, heretofore, been remote for most Americans. A few, such as Leon Campbell, had been aware of the war's impact on observers. George Ensor, a supervisor of a hospital laboratory, had already stopped observing in 1940, acknowledging that at the end of a day, “The work is stiff so I am too tired for anything but bed after my dinner. … Even occultation work has been dropped.”

There seemed to be little doubt; this war would not end as quickly as World War I after the United States entered that conflict, nor with as little engagement from ordinary US citizens. The AAVSO would feel the demands of the war, particularly on its skilled members who were called to assist in war efforts.