DD Form 2401, Civil Aircraft Landing Permit is a form used for obtaining permission for a civil aircraft to use a military airfield for landing. This permit allows landing only, without any other services - like receiving fuel - available from U.S. Army sources.
The latest version of the form - sometimes confused with the DA Form 2401, Organization Control Record for Equipment - was released by the Department of Defense (DoD) in January 2008 with all previous editions being obsolete. An up-to-date DD Form 2401 fillable version is available for digital filing and download below or can be found through the Executive Services Directorate website.
Any civil aircraft located on military airfield grounds should have a copy of the DD 2401. Corporate planes must have a letter from the Contracting Officer's Representative that affirms the requirement to land with their application on hand at all times.