| 14501 | ATLX | Armour Tank Line (Armour Car Lines) | 7/1935 | | NAKINA |
| 14502 | ATLX | Armour Tank Line (Armour Car Lines) | Apr-38 | | NRHS |
| 14503 | ATLX | General American Transportation Corp. | 1/52-4/61 | | NRHS |
| 14504 | ATLX | Armour Car Lines | eliminated 10/58 | | NRHS |
| 14505 | ATLX | General American Transportation Corp. | added 10/58; 7/65 | | NRHS |
| 14506 | ATLX | Armour Tank Line (General American Transportation Corp.) | Oct-66 | | NRHS |
| 14507 | ATLX | General American Transportation Corp. | 4/70; eliminated 7/73 | | NRHS |
| 14508 | ATLX | Atlas Machine & Iron Works, Inc. | added 7/80; eliminated 1/86; 1/94-7/2000 | | NRHS |
| 14509 | ATLX | *ARMOUR TANK LINE (ACL) (GENERAL AMERICAN TRANSPORTATION CORP.) (ELIMINATED 7/1973) | | | PWRC |
| 14510 | ATLX | +ATLAS MACHINE & IRON WORKS, INC. | | | PWRC |
| 14511 | ATLX | Atlas Machine and Iron Works | | | RSRV |
| 14512 | ATLX | ATLAS MACHINE & IRON WORKS, INC. | | | SCAC4 |
| 14513 | ATLX | Atlantic Express | | US-NY | TRAFFIC |
| 14514 | ATLY | A T L INC | | | SCAC3 |
| 14515 | ATLY | ATL | | | SCAC4 |
| 14516 | ATLZ | AMERICAN MARINE INDUSTRIES | | | PWRC |
| 14517 | ATLZ | American Marine Industries | | | RSRV |
| 14518 | ATLZ | ATLANTIC LINES LTD | | | SCAC3 |
| 14519 | ATLZ | AMERICAN MARINE INDUSTRIES | | | SCAC4 |
| 14520 | ATM | Airlines of Tasmania Pty Ltd. | IATA: FO, Callsign: Airtas, Designator IP recalled by IATA | AUS | AVCODES |
| 14521 | ATM | Airlines of Tasmania Pty Ltd. | IATA: IP, Callsign: Airtas, Designator IP recalled by IATA. ICAO designator changed from XAL | AUS | AVCODES |
| 14522 | ATM | Airlines Of Tasmania | IATA: FO | | ICAO1 |
| 14523 | ATM | Azienda Trasporti Milanesi | City: Milano | I | TRAFFIC |
| 14524 | ATMA | ATLAS MARINE SERVICES INC | | | SCAC3 |
| 14525 | ATMA | AUTO TRANSPORTE AMAYA | | | SCAC4 |
| 14526 | ATMB | | City: Bologna | I | TRAFFIC |
| 14527 | ATMC | ATOMIC CARTAGE INC | | | SCAC3 |
| 14528 | ATMC | A TIMELEIGH MOTORCAR | | | SCAC4 |
| 14529 | ATMD | ACTION TRANSFER INC | | | SCAC3 |
| 14530 | ATME | ATLANTIC MARITIME LINES | | | SCAC3 |
| 14531 | ATME | ATHENA MARINE LTD | | | SCAC4 |
| 14532 | ATME | Azienda Transporti di Messina | Real: ATM | I | TRAFFIC |
| 14533 | ATMG | ALLSTATES MOVING INC | | | SCAC4 |
| 14534 | ATMH | ATLANTIC DISTRIBUTION SERVICES INC | | | SCAC4 |
| 14535 | ATMI | ATLAS MARINE | | | SCAC3 |
| 14536 | ATMI | ATLAS MARINE INC | | | SCAC4 |
| 14537 | ATMJ | A T MONITORS | | | SCAC4 |
| 14538 | ATML | ATLANTA MOTOR LINES INC | | | SCAC3 |
| 14539 | ATML | AUTO TRANSPORTES MELGOZA | | | SCAC4 |
| 14540 | ATMM | AIR TRAFFIC MANAGEMENT INC | | | SCAC4 |
| 14541 | ATMN | ALTMAN TRUCKING | | | SCAC3 |
| 14542 | ATMN | ALL TIME TRANSPORT CORP | | | SCAC4 |
| 14543 | ATMO | ATCHISON MOVING & STORAGE | | | SCAC3 |
| 14544 | ATMO | ATMS MOVING SYSTEMS | | | SCAC4 |
| 14545 | ATMP | ATLANTIC MOVERS | | | SCAC3 |
| 14546 | ATMQ | A T M C INC | | | SCAC3 |
| 14547 | ATMR | ATLAS MOTOR EXPRESS, INC | | | SCAC3 |
| 14548 | ATMR | ATLAS MOTOR EXPRESS INC | | | SCAC4 |
| 14549 | ATMS | ATLAS MOVING & STORAGE CO, INC | | | SCAC3 |
| 14550 | ATMS | AUTOMSSA | | | SCAC4 |
| 14551 | ATMT | ATLAS MOTOR EXPRESS, INCORPORATED | | | SCAC3 |
| 14552 | ATMT | | City: Torino | I | TRAFFIC |
| 14553 | ATMU | ATOM ULUSLARARASI NAKLİYAT VE LOJİSTİK HİZMETLERİ A.Ş. | | TR | BIC |
| 14554 | ATMU | MTC ALFA-TRANS CO LTD | | | SCAC4 |
| 14555 | ATMW | AMERICAN TRAILS TRANSPORTATION CO | | | SCAC3 |
| 14556 | ATMX | U.S. Dept. of Energy, Albuquerque Operations Office | added 1/1978; 1/1980-1/1994; eliminated 10/1997; 7/2000-7/2005 (not listed) | | NAKINA |
| 14557 | ATMX | U.S. Atomic Energy Commission, Albequerque Operations Office | 1/1975; eliminated 4/1975 | | NAKINA |
| 14558 | ATMX | United States Energy Research and Development Administration, Albequerque Operations Office | added 4/1975; eliminated 1/1978 | | NAKINA |
| 14559 | ATMX | U.S. Atomic Energy Commission, Albequerque Operations Office | 4/1970 | | NAKINA |
| 14560 | ATMX | U.S. Atomic Energy Commission, Paducah, Kentucky | eliminated 4/1973 | | NAKINA |
| 14561 | ATMX | U.S. Atomic Energy Commission | 4/1961; added 7/1961; added 1/1965; 7/1965; eliminated 7/1965; 10/1966; eliminated 1/1968 | | NAKINA |
| 14562 | ATMX | U.S. Atomic Energy Commission | 1/1950-10/1957 | | NAKINA |
| 14563 | ATMX | U.S. Atomic Energy Commission, care of Union Carbide Nuclear Co., Division of Union Carbide Corp. | added 4/1959 | | NAKINA |
| 14564 | ATMX | U.S. Atomic Energy Commission | 1/52-4/61; added 1/65; 7/65; eliminated 7/65; 10/66; eliminated 1/68 | | NRHS |
| 14565 | ATMX | U.S. Atomic Energy Commission, Albequerque Operations Office | Apr-70 | | NRHS |
| 14566 | ATMX | U.S. Atomic Energy Commission, Paducah, Kentucky | eliminated 4/73 | | NRHS |
| 14567 | ATMX | U.S. Atomic Energy Commission, Albequerque Operations Office | 1/75; eliminated 4/75 | | NRHS |
| 14568 | ATMX | United States Energy Research and Development Administration, Albequerque Operations Office | added 4/75; eliminated 1/78 | | NRHS |
| 14569 | ATMX | U.S. Dept. of Energy, Albuquerque Operations Office | added 1/78; 1/80-1/94; eliminated 10/97; 7/2000 | | NRHS |
| 14570 | ATMX | *PENNSYLVANIA RAILWAY MUSEUM ASSOC. [ARDEN TROLLEY MUSEUM] | | | PWRC |
| 14571 | ATMX | *U.S. ENERGY RESEARCH & DEVELOPMENT ADM. - ALBUQUERQUE OPERATIONS | | | PWRC |
| 14572 | ATMX | United States Department of Energy Albuquerque Operations (Arcelor Mittal Montreal) | | | RSRV |
| 14573 | ATMX | UNITED STATES ATOMIC ENERGY COMMISS | | | SCAC3 |
| 14574 | ATMY | ATLAS MARINE COMPANY | | | SCAC3 |
| 14575 | ATMZ | ATLLAS TIE MILL | | | PWRC |
| 14576 | ATN | Air Transport International LLC | IATA: 8C, Callsign: Air Transport, | USA | AVCODES |
| 14577 | ATN | Air Transport International | IATA: 8C | | ICAO1 |
| 14578 | ATN | Alabama & Tennessee River Railway | | | RSRV |
| 14579 | ATN | ALABAMA AND TENNESSEE RIVER RAILWAY | | | SCAC4 |
| 14580 | ATN | Arriva Trains Northern | 1999: 2043km standard gauge, electrified at 25kV 50Hz Arriva Trains Northern was a train operating company that operated passenger trains in Northern England. The company had previously been known as Northern Spirit before being taken over Arriva. The franchise was taken over by Northern Rail in December 2004. | GB | TRAFFIC |
| 14581 | ATN | Atenon Sp. z o.o. Sp. K. | | PL | VKM |
| 14582 | ATNB | ARMOR TRANSPORTATION INC | | | SCAC3 |
| 14583 | ATNB | A & C TRUCKING LLC | | | SCAC4 |
| 14584 | ATNC | ATLANTIC TRUCKING INCORPORATED | | | SCAC3 |
| 14585 | ATND | ALL TRANSPORT INC | | | SCAC3 |
| 14586 | ATND | ALLSET TRANSPORT LTD | | | SCAC4 |
| 14587 | ATNE | ARAGON TRANSPORTATION ENTERPRISES I | | | SCAC3 |
| 14588 | ATNE | ASTRO OF NEW ENGLAND | | | SCAC4 |
| 14589 | ATNF | AMERICAN TRANS-FREIGHT INC | | | SCAC3 |
| 14590 | ATNG | AMERICAN TRANSFER & STORAGE CO INC | | | SCAC3 |
| 14591 | ATNG | AMERICAN TRANSPORT LOGISTICS | | | SCAC4 |
| 14592 | ATNH | ALUMINUM TRANSPORT INC | | | SCAC3 |
| 14593 | ATNI | AT&T INFORMATION SYSTEM | | | SCAC3 |
| 14594 | ATNI | ANKER TRUCKING INC | | | SCAC4 |
| 14595 | ATNJ | ACTION TRANSPORTATION INC | | | SCAC3 |
| 14596 | ATNK | ALL TRANS INC | | | SCAC3 |
| 14597 | ATNK | ALPHA TANKERS AND FREIGHTERS INTERN | | | SCAC4 |
| 14598 | ATNM | AMERICAN TRAFFIC MANAGEMENT | | | SCAC3 |
| 14599 | ATNM | AUTO TRANSPORTES MEJIA BENAVIDEZ | | | SCAC4 |
| 14600 | ATNN | A T L INC | | | SCAC4 |
