391st

391st may refer to:


 * 391st Bombardment Group, non-flying unit of the Pennsylvania Air National Guard, stationed at Horsham Air National Guard Station
 * 391st Bombardment Squadron, part of the 6th Air Mobility Wing at MacDill Air Force Base, Florida
 * 391st Fighter Squadron (391 FS), part of the 366th Fighter Wing at Mountain Home Air Force Base, Idaho