| 1801 | MCWS | MCW SHIPPING INC | | | SCAC4 |
| 1802 | MCWU | MARINE CONTAINER TEST SERVICES LTD | | GB | BIC |
| 1803 | MCWW | MOELLENBEC | | | SCAC4 |
| 1804 | MCWX | Morton International, Inc. | added 7/1965; 7/1965-10/1966; eliminated 7/1969 | | NAKINA |
| 1805 | MCWX | Morton Salt Co. | added 4/1962; eliminated 7/1965 | | NAKINA |
| 1806 | MCWX | Morton Chemical Co. | added 4/1958; 4/1961; eliminated 4/1962 | | NAKINA |
| 1807 | MCWX | Morton Chemical Co. | 4/61; eliminated 4/62 | | NRHS |
| 1808 | MCWX | Morton Salt Co. | added 4/62; eliminated 7/65 | | NRHS |
| 1809 | MCWX | Morton International, Inc. | added 7/65; 7/65-10/66; eliminated 7/69 | | NRHS |
| 1810 | MCWX | MORTON INTERNATIONAL {MORTON SALT CO.; MORTON CHEMICAL CO.] | | | PWRC |
| 1811 | MCWY | MIDNIGHT COWBOY XPRESS | | | SCAC4 |
| 1812 | MCX | Cargo Express | Callsign: Mauricargo, | RIM | AVCODES |
| 1813 | MCX | Cargo Express | | | ICAO1 |
| 1814 | MCX | The Mead Corp. | 7/1937-7/1954; eliminated 7/1957 | | NAKINA |
| 1815 | MCX | The Mead Corporation | 4/38-1/52 | | NRHS |
| 1816 | MCX | MEAD CORP. | | | PWRC |
| 1817 | MCXB | MEGA COOL EXPRESS INC | | | SCAC4 |
| 1818 | MCXC | MCCLURE TRANSFER LLC | | | SCAC4 |
| 1819 | MCXE | MC EXPRESS INC | | | SCAC4 |
| 1820 | MCXF | MC EXPRESS TRANSPORTS LLC | | | SCAC4 |
| 1821 | MCXG | MAC TRANSPORTATION LTD | | | SCAC4 |
| 1822 | MCXK | MAY & CARTER TRANSPORT INC | | | SCAC4 |
| 1823 | MCXN | MCN EXPRESS INCORPORATED | | | SCAC4 |
| 1824 | MCXP | MERCY EXPRESS | | | SCAC4 |
| 1825 | MCXQ | METRO CITY TRANSPORTATION INC | | | SCAC4 |
| 1826 | MCXU | CARGO LEVANT SCHIFFAHRTSGES M B H | | | SCAC4 |
| 1827 | MCXV | MANTEC EXPRESS LIMITED | | | SCAC4 |
| 1828 | MCY | Ambulance Air Africa | Callsign: Mercy, | ZA | AVCODES |
| 1829 | MCY | Ambulance Air Africa | | | ICAO1 |
| 1830 | MCY | Motley County Ry. Co. | 7/1923 | | NAKINA |
| 1831 | MCY | MOTLEY COUNTY RWY. CO. | | | PWRC |
| 1832 | MCYA | MCCLATCHY BROS INC | | | SCAC4 |
| 1833 | MCYB | MCCLEARY DISTRIBUTING INC | | | SCAC4 |
| 1834 | MCYC | MCCARTY & SONS TOWING & EQUIPMENT T | | | SCAC4 |
| 1835 | MCYD | MID COUNTY COOP | | | SCAC4 |
| 1836 | MCYG | MOTTAS COUNTRY GARDENS INC | | | SCAC4 |
| 1837 | MCYH | MCCOY & SON TRUCKING INC | | | SCAC4 |
| 1838 | MCYI | MCCOY TRANSPORT INC | | | SCAC4 |
| 1839 | MCYL | MCCULLEY OIL CO INC | | | SCAC4 |
| 1840 | MCYN | MOTOR CITY AUTO TRANSPORT INC | | | SCAC4 |
| 1841 | MCYO | MCCLYMOND | | | SCAC4 |
| 1842 | MCYT | MCCARTHY TRANSFER AND STORAGE | | | SCAC4 |
| 1843 | MCYV | MERCURY SERVICES INCORPORATED | | | SCAC4 |
| 1844 | MCYY | MARCEY OIL COMPANY INC | | | SCAC4 |
| 1845 | MCZ | MONSANTO CORPORATION | | | PWRC |
| 1846 | MCZQ | MCC CONTRACTING INC | | | SCAC4 |
| 1847 | MCZU | MINISTRY OF DEFENCE OF THE CZECH REPUBLIC | | CZ | BIC |
| 1848 | MCZU | MINISTRY OF DEFENCE OF THE CZECH RE | | | SCAC4 |
| 1849 | MD | Air Madagascar | ICAO: MDG, Callsign: Air Madagascar, IATA Prefix: 258, ICAO callsign changed from Madair | RM | AVCODES |
| 1850 | MD | Air Madagascar | ICAO: MDG, Callsign: Madair, IATA Prefix: 258, ICAO callsign changed to Air Madagascar | RM | AVCODES |
| 1851 | MD | FIM Air Ltd. | ICAO: FMI, Callsign: First Myanmar, ICAO callsign changed to Gecko. | MYA | AVCODES |
| 1852 | MD | C&J R.R. Co. d/b/a Mississippi Delta R.R. | 7/2005; eliminated 1/2010 | | NAKINA |
| 1853 | MD | Municipal Docks | 1/1980 | | NAKINA |
| 1854 | MD | Municipal Docks Ry. of the Jacksonville Port Authority | 1/1975 | | NAKINA |
| 1855 | MD | Municipal Docks Ry. of the Jacksonville Port Authority | Jan-75 | | NRHS |
| 1856 | MD | Municipal Docks | Jan-80 | | NRHS |
| 1857 | MD | *MUNICIPAL DOCKS RAILWAY, JACKSONVILLE PORT AUTHORITY (FLORIDA) | | | PWRC |
| 1858 | MD | +C & J RAILROAD CO. d/b/a MISSISSIPPI DELTA RAILROAD | | | PWRC |
| 1859 | MD | Municipal Docks | | | RSRV |
| 1860 | MD | MISSISSIPPI DELTA RAILROAD (C&J RAI | | | SCAC4 |
| 1861 | MD | Maryland - Delaware | | USA | TRAFFIC |
| 1862 | MD&S | Macon, Dublin & Savannah R.R. Co. | 8/1920-10/1957 | | NAKINA |
| 1863 | MD&S | Macon, Dublin & Savannah R.R. Co. | 4/38-10/57 | | NRHS |
| 1864 | MD&S | MACON, DUBLIN & SAVANNAH RAILROAD CO. | | | PWRC |
| 1865 | MDA | Mandarin Airlines Ltd. | IATA: AE, Callsign: Mandarin, IATA Prefix: 803, | RC | AVCODES |
| 1866 | MDA | Mandarin Airlines | IATA: AE | | ICAO1 |
| 1867 | MDAA | MD TRUCKING | | | SCAC4 |
| 1868 | MDAC | MIDDLE ATLANTIC PRODUCTS INC | | | SCAC4 |
| 1869 | MDAD | MIDDLEBURG PROPERTIES LIMITED | | | SCAC4 |
| 1870 | MDAD | Miami Dade Aviation Department | | USA | TRAFFIC |
| 1871 | MDADE | Miami-Dade Transit | | USA | TRAFFIC |
| 1872 | MDAE | MARTINEZ, DORA E | | | SCAC4 |
| 1873 | MDAF | MID AMERICA FREIGHT SYSTEMS LTD | | | SCAC4 |
| 1874 | MDAI | MAINLAND TRANSPORT LTD | | | SCAC4 |
| 1875 | MDAM | M & D TRUCKING CO INC | | | SCAC4 |
| 1876 | MDAO | MID-ATLANTIC LOGISTICS COMPANY | | | SCAC4 |
| 1877 | MDAQ | MDI TRANSPORTATION SYSTEMS INC | | | SCAC4 |
| 1878 | MDAS | MIDAS EXPRESS, INC | | | SCAC1 |
| 1879 | MDAS | MIDWAY TRANSPORTATION INC | | | SCAC4 |
| 1880 | MDAU | MEDAFRICA LINE S P A | | | SCAC4 |
| 1881 | MDAW | MODEL DAIRY LLC | | | SCAC4 |
| 1882 | MDAX | Merchants Despatch Transportation Co. | added 1/1962; 7/1965-1/1980; eliminated 7/1985 | | NAKINA |
| 1883 | MDAX | Merchants Despatch Transportation Co. | added 1/62; 7/65-1/80 | | NRHS |
| 1884 | MDAX | MERCHANTS DESPATCH TRANSPORTATION CORP. | | | PWRC |
| 1885 | MDAX | Merchants Despatch Transportation Corporation | | | RSRV |
| 1886 | MDAY | MOLIVA DENIZCILIK AS | | | SCAC4 |
| 1887 | MDAZ | MERIDIAN AGGREGATES | | | PWRC |
| 1888 | MDB | Monde Air Charters Ltd. | Callsign: Mondeair Cargo, | GB | AVCODES |
| 1889 | MDB | Vertical Aviation, LLC | Callsign: Marianas, | USA | AVCODES |
| 1890 | MDB | Monde Air Charters | | | ICAO1 |
| 1891 | MDBA | MARINER DISTRIBUTING COMPANY AND ANCHOR DISTRIBUTING COMPANY | | | SCAC1 |
| 1892 | MDBA | MDT | | | SCAC4 |
| 1893 | MDBB | MCLAMB, DENNIS INC | | | SCAC4 |
| 1894 | MDBD | MCBRIDES DELIVERY SYSTEMS INC | | | SCAC4 |
| 1895 | MDBF | MCRAE, D & A INC | | | SCAC4 |
| 1896 | MDBL | MAD DOG BROKERAGE INC | | | SCAC4 |
| 1897 | MDBM | MEDBULK MARITIME | | | SCAC4 |
| 1898 | MDBN | MASON AND DIXON LINES | | | SCAC4 |
| 1899 | MDBT | MDB TRANSPORTATION | | | SCAC4 |
| 1900 | MDBU | MED BOX SL | | | SCAC4 |
