3F is an Air Force Specialty Code (AFSC) that stands for Force Support. Airmen in this field perform all personnel functions, including:
Providing information about Air Force personnel and dependents benefits and entitlements
Some specific jobs in the 3F field include:
3F071: Performs Personnel Support for Contingency Operations (PERSCO) functions
3F0X1: Analyzes Department of Defense and Department of the Air Force policy and provides recommendations to commanders, supervisors, Airmen and Guardians
3F0X1: Manages, supervises, and leads military personnel and human resource programs
An RE-3F reenlistment code means that an individual has a situation that will require a waiver before they can re-enlist. This could be anything from a medical issue to a legal matter to a paperwork SNAFU.