Locomotive Classification
There are two main types of steam locomotive classification. The first one is the Whyte Classification System which is named after Frederick Methvan Whyte, a New York Central Railroad mechanical engineer. The first number in the system tells the total number of leading wheels, the middle numbers tells the total number of driving wheels, and the last number tells the total number of trailing wheels.
The other classification is the UIC System. UIC is a French abbreviation for "Union Internationale des Chemins de fer" or "International Union of Railways" in English. In this system, unpowered axles get a number such as 1 for one axle, 2 for two axles, etc. Driving axles get a letter such as A for one axle, B for two axles, etc. Trucks get a number and an apostrophy such as 1' for a one axle truck, 2' for a two axle truck, etc.
The advantage of the UIC over the Whyte, is that the UIC transitions easily from steam to diesel locomotives.
| Whyte | UIC | Engine Diagram (Side View) | Nickname |
| 0-2-2-0 | A-A | O-O | Compound |
| Not Known | A-3-A | O-ooo-O | Petiet |
| 0-4-0 | B | OO | 4-Wheel Switcher |
| 0-4-4 | B-2' | OO-oo | Forney |
| Not Known | B1A | OOoO | Not Known |
| 0-6-0 | C | OOO | 6-Wheel Switcher |
| 0-6-2 | C-1' | OOO-o | Not Known |
| 0-6-6-0 | C-C | OOO-OOO | Compound |
| 0-6-6-6-6-0 | C-C-C-C | OOO-OOO-OOO-OOO | Jawn Henry Steam Turbine |
| 0-8-0 | D | OOOO | 8-Wheel Switcher |
| 0-8-2 | D-1' | OOOO-o | Not Known |
| 0-8-8-0 | D-D | OOOO-OOOO | Angus |
| 0-10-0 | E | OOOOO | 10-Wheel Switcher |
| 0-10-2 | E-1' | OOOOO-o | Union |
| 0-12-0 | F | OOOOOO | 12-Wheel Switcher |
| 2-2-0 | 1'-A | o-O | Planet |
| 2-2-2 | 1'-A-1' | o-O-o | Single |
| 2-4-0 | 1'-B | o-OO | Porter |
| 2-4-2 | 1'-B-1' | o-OO-o | Columbia |
| 2-4-4-2 | 1'-B-B-1' | o-OO-OO-o | Not Known |
| 2-6-0 | 1'-C | o-OOO | Mogul |
| 2-6-2 | 1'-C-1' | o-OOO-o | Prairie |
| 2-6-4 | 1'-C-2' | o-OOO-oo | Adriatic |
| 2-6-6-0 | 1'-C-C | o-OOO-OOO | Not Known |
| 2-6-6-2 | 1'-C-C-1' | o-OOO-OOO-o | Compound |
| 2-6-6-4 | 1'-C-C-2' | o-OOO-OOO-oo | Not Known |
| 2-6-6-6 | 1'-C-C-3' | o-OOO-OOO-ooo | Allegheny |
| 2-6-8-0 | 1'-C-D | o-OOO-OOOO | Not Known |
| 2-8-0 | 1'-D | o-OOOO | Consolidation |
| 2-8-2 | 1'-D-1' | o-OOOO-o | Mikado |
| 2-8-4 | 1'-D-2' | o-OOOO-oo | Berkshire |
| 2-8-8-0 | 1'-D-D | o-OOOO-OOOO | Bull Moose |
| 2-8-8-2 | 1'-D-D-1' | o-OOOO-OOOO-o | Chesapeake |
| 2-8-8-4 | 1'-D-D-2' | o-OOOO-OOOO-oo | Yellowstone |
| 2-8-8-8-2 | 1'-D-D-D-1' | o-OOOO-OOOO-OOOO-o | Erie Triplex |
| 2-8-8-8-4 | 1'-D-D-D-2' | o-OOOO-OOOO-OOOO-oo | Virginian Triplex |
| 2-10-0 | 1'-E | o-OOOOO | Decapod |
| 2-10-2 | 1'-E-1' | o-OOOOO-o | Santa Fe |
| 2-10-4 | 1'-E-2' | o-OOOOO-oo | Texas |
| 2-10-10-2 | 1'-E-E-1' | o-OOOOO-OOOOO-o | Not Known |
| 2-12-0 | 1'-F | o-OOOOOO | Centipede |
| 2-12-2 | 1'-F-1' | o-OOOOOO-o | Javanic |
| 2-12-4 | 1'-E-2' | o-OOOOOO-oo | Bulgarian Class 46 |
| 4-2-0 | 2'-A | oo-O | Jervis |
| 4-2-2 | 2'-A-1' | oo-O-o | Bicycle |
| 4-4-0 | 2'-B | oo-OO | American |
| 4-4-2 | 2'-B-1' | oo-OO-o | Atlantic |
| 4-4-4 | 2'-B-2' | oo-OO-oo | Reading |
| 4-4-4-4 | 2'-B-B-2' | oo-OO-OO-oo | Duplex |
| 4-4-6-4 | 2'-B-C-2' | oo-OO-OOO-oo | Duplex-Drive |
| 4-6-0 | 2'-C | oo-OOO | Ten-Wheeler |
| 4-6-2 | 2'-C-1' | oo-OOO-o | Pacific |
| 4-6-4 | 2'-C-2' | oo-OOO-oo | Hudson |
| 4-6-4-4 | 2'-C-B-2' | oo-OOO-OO-oo | Duplex-Drive |
| 4-6-6-2 | 2'-C-C-1' | oo-OOO-OOO-o | Cab Forward |
| 4-6-6-4 | 2'-C-C-2' | oo-OOO-OOO-oo | Challenger |
| 4-6-6-4 | 2'-C-C-2' | oo-OOO-OOO-oo | Steam Turbine |
| 4-8-0 | 2'-D | oo-OOOO | Twelve-Wheeler |
| 4-8-2 | 2'-D-1' | oo-OOOO-o | Mountain |
| 4-8-4 | 2'-D-2' | oo-OOOO-oo | Northern |
| 4-8-8-2 | 2'-D-D-1' | oo-OOOO-OOOO-o | Cab Forward |
| 4-8-8-4 | 2'-D-D-2' | oo-OOOO-OOOO-oo | Big Boy |
| 4-10-0 | 2'-E | oo-OOOOO | Mastodon |
| 4-10-2 | 2'-E-1' | oo-OOOOO-o | Southern Pacific |
| 4-12-2 | 2'-F-1' | oo-OOOOOO-o | Union Pacific |
| 4-14-4 | 2'-G-2' | oo-OOOOOOO-oo | Russian AA20 |
| 6-2-0 | 3'-A | ooo-O | Crampton |
| 6-4-4-6 | 3'-B-B-3' | ooo-OO-OO-ooo | Pennsylvania |
| 6-8-6 | 3'-D-3' | ooo-OOOO-ooo | Steam Turbine |
| Not Known | 2'-C1-2'-C1-B | oo-OOOo-oo-OOOo-OO | Steam Turbine |