What is required for a US airport listed in the IFR Enroute Supplement to meet operational requirements?

For a U.S. airport to be listed in the IFR Enroute Supplement and meet operational requirements, it is necessary to have a published Department of Defense (DoD) Instrument Approach Procedure. This requirement ensures that the airport has specific procedures established that comply with military standards, facilitating the safe and efficient operation of military aircraft during instrument flight scenarios. The inclusion of a published approach procedure is crucial because it allows pilots to follow standardized routes and descend safely to the runway, adhering to the demanding safety and operational standards expected in military aviation.

In contrast, the other options, while they may relate to military operations, do not directly pertain to the criteria for inclusion in the IFR Enroute Supplement. Permission for transient military aircraft pertains to the access policy rather than operational requirements. An operational control tower is not a prerequisite for all airports within the IFR Enroute Supplement, as some may operate without one. Similarly, dedicated military runways are specific to certain installations but are not universally required for airports included in the IFR Enroute Supplement. Therefore, the presence of a published DoD Instrument Approach Procedure stands out as the primary and necessary condition.