| 201 | UBTX | Union Bag-Camp Paper Corp. | added 10/1956; 10/1957-7/1965; eliminated 7/1966 | | NAKINA |
| 202 | UBTX | Union Camp Corp. | added 7/1966; 10/1966-1/1980; eliminated 10/1987 | | NAKINA |
| 203 | UBTX | Union Bag & Paper Corp. | added 7/55 | | NRHS |
| 204 | UBTX | Union Bag-Camp Paper Corp. | 10/57-7/65; eliminated 7/66 | | NRHS |
| 205 | UBTX | Union Camp Corp. | added 7/66; 10/66-1/80; eliminated 10/87 | | NRHS |
| 206 | UBTX | UNION CAMP CORP. [UNION BAG & PAPER CORP.] | | | PWRC |
| 207 | UBTX | Union Camp Corporation | | | RSRV |
| 208 | UBTX | UNION BAY-CAMP PAPER CORP | | | SCAC4 |
| 209 | UC | LADECO Cargo, S.A. | ICAO: LDC, Callsign: Ladeco Cargo, IATA Prefix: 527, Designator UC recalled by IATA | RCH | AVCODES |
| 210 | UC | Ladeco S.A. d/b/a Ladeco Airlines | ICAO: LCO, Callsign: Ladeco, IATA Prefix: 145, Name changed to LANExpress 01 November 2001. | RCH | AVCODES |
| 211 | UC | Ladeco S.A. d/b/a LANExpress | ICAO: LCO, Callsign: Ladeco, IATA Prefix: 145, Name changed from Ladeco S.A. d/b/a Ladeco Airlines | RCH | AVCODES |
| 212 | UC | Linea Aerea del Cobre Ltda. (LADECO) | ICAO: UCO, Callsign: Ladeco, | RCH | AVCODES |
| 213 | UC | LAN Cargo S.A. d/b/a LATAM Cargo Chile | ICAO: LCO, IATA Prefix: 527, Name changed from LAN Cargo S.A. w.e.f. 05 May 2016. | RCH | AVCODES |
| 214 | UCA | Champlain Enterprises, LLC. t/a CommutAir | IATA: C5, Callsign: Commutair, IATA Prefix: 841, Name changed from Commutair (US Airways Express) | USA | AVCODES |
| 215 | UCA | Commutair / US Airways Express | Callsign: Commutair, Name changed to Champlain Enterprises Inc. | USA | AVCODES |
| 216 | UCA | CommutAir | IATA: C5 | | ICAO1 |
| 217 | UCAG | UNITED CARGO LINES | | | SCAC4 |
| 218 | UCAL | UTI CRAF AGENT | | | SCAC4 |
| 219 | UCAR | UPSTATE AIR CARGO | | | SCAC4 |
| 220 | UCAT | USA CARTERET LLC | | | SCAC4 |
| 221 | UCAU | UCA CONTAINERS AG | | | PWRC |
| 222 | UCAU | UCA Containers AG | | | RSRV |
| 223 | UCAU | UNITED ARAB SHIPPING CO SAG | | | SCAC4 |
| 224 | UCAW | UNI-CHARTERING A/S | | | SCAC4 |
| 225 | UCB | United Caribbean Airlines B.V. | IATA: 4J, Callsign: Eagle Eye, Name changed to United Caribbean Airlines B.V. d/b/a JetAir Caribbean. | CUR | AVCODES |
| 226 | UCB | United Caribbean Airlines B.V. d/b/a JetAir Caribbean | IATA: 4J, Callsign: Eagle Eye, Name changed to Jetair Caribbean B.V. ICAO Designator changed to JRC. Name changed from United Caribbean Airlines B.V. | CUR | AVCODES |
| 227 | UCBC | UNION CITY BODY CO | | | SCAC4 |
| 228 | UCBX | United Carbon Co., Inc. | 7/1935-4/1961; eliminated 10/1963 | | NAKINA |
| 229 | UCBX | United Carbon Co. | added 10/1963; 7/1965-10/1966; eliminated 1/1969 | | NAKINA |
| 230 | UCBX | Ashland Chemical Co., Division of Ashland Oil & Refining Co., Carbon Black & Synthetic Rubber Division | added 1/1969; 4/1970; eliminated 4/1971 | | NAKINA |
| 231 | UCBX | Ashland Chemical Co., Division of Ashland Oil Inc., Carbon Black & Synthetic Rubber Division | added 4/1971; eliminated 7/1971 | | NAKINA |
| 232 | UCBX | Ashland Chemical Co., Division of Ashland Oil Inc. | added 7/1971; 1/1975; eliminated 1/1976 | | NAKINA |
| 233 | UCBX | United Carbon Co., Inc. | 4/38-10/66; eliminated 1/69 | | NRHS |
| 234 | UCBX | Ashland Chemical Co., Division of Ashland Oil & Refining Co., Carbon Black & Synthetic Rubber Division | added 1/69; 4/70; eliminated 4/71 | | NRHS |
| 235 | UCBX | Ashland Chemical Co., Division of Ashland Oil Inc., Carbon Black & Synthetic Rubber Division | added 4/71 | | NRHS |
| 236 | UCBX | Ashland Chemical Co., Division of Ashland Oil Inc. | Jan-75 | | NRHS |
| 237 | UCBX | ASHLAND CHEMICAL CO., CARBON BLACK & SYNTHETIC RUBBER DIV. [UNITED CARBON CO.] | | | PWRC |
| 238 | UCBZ | UNITED COOP OF BIGELOW | | | PWRC |
| 239 | UCC | Uganda Air Cargo | Callsign: Uganda Cargo, | EAU | AVCODES |
| 240 | UCC | Uganda Air Cargo | | | ICAO1 |
| 241 | UCC | UNION CARBIDE CORPORATION, CARBON PRODUCTS DIV. | | | PWRC |
| 242 | UCCB | US CARRIERS CORP | | | SCAC4 |
| 243 | UCCE | ULTIMATE CONTAINER CARRIER | | | SCAC4 |
| 244 | UCCP | US CARGO CORP | | | SCAC4 |
| 245 | UCCS | UPPER COLUMBIA CONFERENCE SDA | | | SCAC4 |
| 246 | UCCU | AMERICAN CYANAMID | | | PWRC |
| 247 | UCCU | American Cyanamid | | | RSRV |
| 248 | UCCX | Utah Copper Corp. | 7/1937 (not listed) | | NAKINA |
| 249 | UCCX | United Contracting Co. | 4/1947-4/1961 (not listed) | | NAKINA |
| 250 | UCCX | Union Carbide Canada Ltd. | added 10/1969; 4/1970-1/1980; eliminated 1/1985; 1/1994-7/2005 (not listed) | | NAKINA |
| 251 | UCCX | United Contracting Co. | 1/52-4/61 | | NRHS |
| 252 | UCCX | Union Carbide Canada Ltd. | added 10/69; 4/70-1/80; eliminated 1/85; 1/94-7/2000 | | NRHS |
| 253 | UCCX | *UTAH COPPER CORP. | | | PWRC |
| 254 | UCCX | *UNITED CONTRACTING CO. | | | PWRC |
| 255 | UCCX | +UNION CARBIDE CANADA, LTD. | | | PWRC |
| 256 | UCCX | Union Carbide Canada | | | RSRV |
| 257 | UCCX | UNION CARBIDE CORP. OF CANADA | | | SCAC4 |
| 258 | UCCZ | UNION CAMP CORP. | | | PWRC |
| 259 | UCDU | UNIVERSAL INC CONTAINERS TRADING LLC | | UAE | BIC |
| 260 | UCEA | USA CARRIER ENTERPRISES LLC | | | SCAC4 |
| 261 | UCEN | UNITED CARTAGE INC | | | SCAC4 |
| 262 | UCEX | Union Electric Co. | added 10/1980; eliminated 10/1984; 1/1994 (not listed); added 1/1997; eliminated 4/1997; 7/2000-7/2005 (not listed) | | NAKINA |
| 263 | UCEX | Union Electric Co. | added 10/80; eliminated 10/84; 1/94; added 1/97; eliminated 4/97; 7/2000 | | NRHS |
| 264 | UCEX | UNION ELECTRIC COMPANY | | | PWRC |
| 265 | UCEX | Union Electric | | | RSRV |
| 266 | UCEX | UNION ELECTRIC COMPANY | | | SCAC4 |
| 267 | UCFN | UNITED CALIFORNIA FREIGHT SOLUTIONS | | | SCAC4 |
| 268 | UCFX | Union Carbide Corp., Chemicals and Plastics Operations Division | added 4/1971; 1/1975; eliminated 1/1979 | | NAKINA |
| 269 | UCFX | Union Carbide Corp., Chemicals and Plastics Division | added 1/1979; 1/1980; eliminated 7/1980 | | NAKINA |
| 270 | UCFX | Union Carbide Corp. | added 7/1980; eliminated 10/1980 | | NAKINA |
| 271 | UCFX | Union Carbide Corp., Chemicals and Plastics Division | added 10/1980; eliminated 5/1983 | | NAKINA |
| 272 | UCFX | Union Carbide Corp. | added 5/1983; eliminated 1/1993 | | NAKINA |
| 273 | UCFX | Union Carbide Chemicals and Plastics Co., Inc. | added 1/1993; 1/1994; eliminated 1/1995; eliminated 4/1995 | | NAKINA |
| 274 | UCFX | Union Carbide Corp. | added 1/1995; added 4/1995; 7/2000-7/2005 | | NAKINA |
| 275 | UCFX | Union Carbide Corp., Chemicals and Plastics Operations Division | added 4/71; 1/75; eliminated 1/79 | | NRHS |
| 276 | UCFX | Union Carbide Corp., Chemicals and Plastics Division | added 1/79; 1/80; eliminated 7/80 | | NRHS |
| 277 | UCFX | Union Carbide Corp. | added 7/80; eliminated 10/80 | | NRHS |
| 278 | UCFX | Union Carbide Corp., Chemicals and Plastics Division | added 10/80; eliminated 5/83 | | NRHS |
| 279 | UCFX | Union Carbide Corp. | added 5/83; eliminated 1/93 | | NRHS |
| 280 | UCFX | Union Carbide Chemicals and Plastics Co., Inc. | added 1/93; 1/94; eliminated 1/95; eliminated 4/95 | | NRHS |
| 281 | UCFX | Union Carbide Corp. | added 1/95; added 4/95; 7/2000 | | NRHS |
| 282 | UCFX | UNION CARBIDE CORP., SUBSIDIARY OF THE DOW CHEMICAL CO. U.S.A. | | | PWRC |
| 283 | UCFX | Union Carbide Corporation | | | RSRV |
| 284 | UCFX | UNION CARBIDE CORPORATION (A SUBSID | | | SCAC4 |
| 285 | UCG | Uniworld Commercial Group, S.A. (Uniworld Air Cargo) | IATA: U7, Callsign: Uniworld, IATA Prefix: 399, | PA | AVCODES |
| 286 | UCGL | UNITED CONCRETE & GRAVEL LTD | | | SCAC4 |
| 287 | UCGO | UNICARGO TRANSPORT | | | SCAC4 |
| 288 | UCGU | UCGU CONTAINERS DI UCCELLINI VALTER | | | SCAC4 |
| 289 | UCH | US Airports Air Charter | Callsign: US Charter, | USA | AVCODES |
| 290 | UCH | US Airports Air Charter | | | ICAO1 |
| 291 | UCHL | UNLIMITED CHANNELS | | | SCAC4 |
| 292 | UCHN | UCHAN TRANSPORT (1987) LTD | | | SCAC4 |
| 293 | UCIA | UNION COMMERCIAL INCORPORATED | | | SCAC4 |
| 294 | UCIC | ULYSESS CARRIERS INC | | | SCAC4 |
| 295 | UCINA | TECHNOSTEEL LBR SRL | | RO | VKM |
| 296 | UCIQ | UNLIMITED CARRIER INC | | | SCAC4 |
| 297 | UCIR | Union County Industrial R.R. Co. | added 7/1996; 7/2000-7/2005 | | NAKINA |
| 298 | UCIR | Union County Industrial R.R. Co. | added 7/96; 7/2000 | | NRHS |
| 299 | UCIR | UNION COUNTY INDUSTRIAL RAILROAD CO. | | | PWRC |
| 300 | UCIR | Union County Industrial Railroad | | | RSRV |
