Academy Superintendent Lt. Gen. Michelle Johnson said the change was made to respect cadets' freedom of religion.
The oath states, "We will not lie, steal or cheat, nor tolerate among us anyone who does. Furthermore, I resolve to do my duty and to live honorably, so help me God."
Cadets are required to take the oath once a year, academy spokesman Maj. Brus Vidal said.
Mikey Weinstein, founder and president of the Military Religious Freedom Foundation, welcomed the change but questioned how it will be applied.
If the person leading the oath includes the words, cadets who choose not to say them might feel vulnerable to criticism, he said.
"What does it mean, 'optional'?" Weinstein said. "The best thing is to eliminate it."
Vidal said the oath is led by the Cadet Wing honor chair, a student, and that person will also have the option to use or not use the words.
Academy officials did not immediately return a follow-up call seeking comment on Weinstein's question.
The West Point equivalent oath does not include the words "so help me God," said Frank DeMaro, a school spokesman. It states, "A cadet will not lie, cheat or steal, or tolerate those who do."
Officials at the U.S. Naval Academy did not immediately return a call. "The Honor Concept" on the Naval Academy website includes similar proscriptions against lying, cheating and stealing but includes no religious reference.
The Air Force Academy outside Colorado Springs has about 4,000 cadets. When they graduate, they are commissioned as second lieutenants.
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