Don’t know if it’s changed, but I once took a flight to Guam from Hawaii on business and was not asked for my passport (Which I did not have with me) until I was boarding the return flight in Agana. SURPRISE!
Five places you can go without a U.S. passport
1. Puerto Rico.
2. United States Virgin Islands.
3. Northern Mariana Islands.
4. Guam.
5. American Samoa.
Guam from Hawaii
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I believe Guam is a US Territory, just like the US Virgin Islands...no passport required.
Of course none of our soldiers who landed on D-Day needed one either, unlike today.