Some individual airlines allow this sort of thing. As far as I know, American Express does not explicitly allow military service members free access to their lounges … directly. However, certain AMEX cards (Platinum personal and Platinum business) do come with “free” Centurion Lounge access.
U.S. military personnel traveling in uniform can access domestic and international American Airlines Admirals Club locations, with the exception of the Airspace Lounge in San Diego (SAN) and the JAL Sakura Lounge in Honolulu (HNL).
Valid Delta Sky Club Membership and a same-day boarding pass required (only one credential may be used for Club access). Individuals must be at least 18 years of age for Club Membership to access without a responsible, supervising adult. Must be at least 21 years of age to enjoy alcoholic beverages.
Airport lounge access requires a membership, day pass or qualifying airline ticket. Business and first-class passengers often get free access to airline lounges, as do elite members and some U.S. military personnel.
USO airport lounges are made to provide comfort to the military community on their journeys, no matter where they're going. At these lounges, which can be located before or after TSA security checkpoints, service members can find everything from free snacks and coffee to a comfy chair to take a quick nap.
Access: To use USO facilities, you need to have a current Active Duty, Guard, Reserve or Dependent ID card. We also accept military retiree ID cards if space is available. For reference though, VA issued ID cards or driver's licenses with Veteran shown on the card do not fall into the above categories.
For starters, they're exclusively for passengers traveling in Polaris business class on United (or business or first class on a Star Alliance flight) for a long-haul international flight. These lounges offer dining through a hot and cold buffet, as well as drinks like wine, spirits, craft beer and cocktails.
Passengers with AirPass membership, First and Business Class MileSAAver award tickets and AAnytime award tickets may also fly standby. Complimentary standby is also available for active U.S. military personnel traveling on orders or personal travel and active U.S. military dependents traveling on orders.