[3] While serving as the chief of staff of the Hawaiian Department, Hayes warned of the possibility of a sneak attack on Pearl Harbor by Japan.

In standing orders to the department, Hayes wrote: "It is possible that a declaration of war upon the United States may be preceded by a surprise raid or attack on the Pearl Harbor Naval Base by hostile aircraft, submarines, or surface ships".

[4] Hayes was transferred back to the mainland in late November 1941, due to a scheduled rotation,[5] and stationed at Fort Bragg.

From December 1941 to March 1942 Hayes briefly served as the professor of Military Science and Tactics at Harvard University.

[10] On August 3, 1944, under the provisions of the Smith-Connally Act, President Franklin Roosevelt signed an order authorizing the U.S. military's takeover of the Philadelphia Transportation Company.

The strike paralyzed the public transportation system in Philadelphia and significantly disrupted the war production in the city.

After brief negotiations, Hayes issued an ultimatum on August 5 that those strikers who would not return to work by August 7, would be fired and refused the War Manpower Commission job availability certificates for the duration of the war, and that those between ages of 18 and 37 would also lose their military draft deferments.

[11] For his role in quickly bringing the Philadelphia strike to an end, Gen. Hayes was later awarded a Legion of Merit.