Union Pacific Steam Locomotives
This page was last updated on March 6, 2010.
General Information
(Based on an original completed in April 1996; updated in August 1998; with additional updates starting in March 2009)
Steam Locomotive Index
- Classes and Class Designations
- Named Locomotives (separate page)
- Compound Locomotives
- Wootten Fireboxes and Camelback Cabs
- Belpaire Fireboxes
- Tractive Force and Horsepower
- Wheel Arrangements
- Bibliography (separate page)
Classes and Class Designations
On Union Pacific, there were two similar but different series of locomotive Classes, also known as Class Designations or Classifications. Locomotive classes were shown in UP's locomotive folio diagram sheets, in the Accounting Department's Form 70 "List Of Agencies, Stations, Equipment, Etc.", and on the locomotive cab sides.
The original classes started in the Harriman Common Standard era, and were first shown on painting and lettering sheets dated 1904. These were the CS classes such as MK-1, MK-2, etc., where a wheel type was designated (C for Consolidation, and MK for Mikado, etc.), with a trailing sequential number. These designations were not used on the locomotives' cab sides, and apparently went away during the 1930s.
The cab side lettering instead included the classes without the sequential number, using the more common class and driver size combination. An example would be the Common Standard Mikados MK-1 and MK-2, both becoming MK-57, or the WWII era MacA-57.
The cab side lettering started in 1937. (see Jim Ehernberger's article in The Streamliner, Volume 8, Number 1)
Compound Locomotives
The following comes from George Drury's Guide to North American Steam Locomotives (Kalmbach, 1993)
In 1889 Samuel Vauclain of Baldwin Locomotive Works patented a four-cylinder compound system, and Baldwin built the first of the type, a 4-4-0 for the Baltimore & Ohio. The Vauclain compound had two cylinders on each side: a high-pressure cylinder and a low-pressure cylinder. Usually the small high-pressure cylinder was on top; on low-drivered freight locomotives the low-pressure cylinder was on top for clearance reasons. The diameter of the low-pressure cylinder was about 1.7 times that of the high-pressure cylinder. The two cylinders, a valve chamber, and half the cylinder saddle were cast in a single piece.
A single valve on each side fed steam from the boiler to the high-pressure cylinder and from there to the low-pressure cylinder. The two pistons drove on a common crosshead. The engine could be worked simple — boiler pressure in all four cylinders — for starting. On the whole the design was successful. By 1904, when it was superseded by the balanced compound, Baldwin had built more than 2,000 Vauclain compound locomotives.
Compound engines worked well in stationary power plants and in steamships, where triple-expansion engines were common and quintuple-expansion engines weren't unheard of. In these applications they were low-speed engines, and they ran better when the valves for each stage could be controlled independently — and that task was easier for an engineer who was concerned only with running a stationary engine and did not have to watch for signals, curves, washouts, stations, and cows on the track.
One of the fundamental dilemmas in the design of a steam locomotive concerns the use of exhaust steam to create a draft for the fire. It does that by passing through a nozzle in the smokebox, working on the same principle as an atomizer or spray gun. The more restrictive the nozzle, the better the draft — and the more back pressure in the cylinder. The greater the amount of energy used to create the draft, the less energy will be available to move the train.
Another problem is that of condensation. As steam expands in the cylinder, some of it condenses into water. If the cylinder is hot and the initial steam pressure is high, the problem is almost nonexistent, but if the cylinder is cold and the pressure is low, the water, being incompressible, can damage the piston and cylinder head.
The draft and condensation problems were worse on compound locomotives. By the time steam had pushed the high-pressure piston to the other end of the cylinder, passed through the valves and the pipes to the low-pressure cylinder, and pushed that piston the length of the cylinder, it had very little pressure but a great deal of volume. With little energy left in the steam, exhausting the cylinder took longer, and there was less energy available to create the required draft.
The superheater delivered the efficiency that compounding only promised. It was a simple, no-moving-parts affair, an arrangement of pipes in the smokebox that intercepted steam on its route from steam dome to cylinders and shuttled it back through the firetubes of the boiler, where it absorbed more heat and therefore more energy.
(Wikipedia article about Vauclain four-cylinder compound locomotives) (includes a link to the original June 1889 patent)
Schenectady built the following two-cylinder cross-compound locomotives for Union Pacific; all were rebuilt on the dates shown:
| First Numbers |
Type | Quantity | Builder | Date Built |
Date Rebuilt To Simple |
Later Numbers |
| UP 1320 (2nd), 1321 (2nd) | 2-8-0 | 2 | Schenectady | 1898 | 1909 | UP 119, 120 |
Baldwin built the following Vauclain compound locomotives for Union Pacific (and its subsidiaries); all were rebuilt to simple on the dates shown:
| First Numbers |
Type | Quantity | Builder | Date Built |
Date Rebuilt To Simple |
Later Numbers |
| UP 1621-1680 | 2-8-0 | 60 | Baldwin | 1900 | 1910-1912 | UP 400-459 |
| UP 1820-1869 | 4-6-0 | 50 | Baldwin | 1900-1903 | 1912-1918 | UP 1320-1369 |
| UP 1680-1699 | 2-8-0 | 20 | Baldwin | 1901 | 1910-1912 | UP 460-479 |
| OSL 770-777 | 2-6-0 | 8 | Baldwin | 1901 | 1911-1913 | OSL 4100-4107 |
| OSL 950-964 | 2-8-0 | 15 | Baldwin | 1901 | 1911 | OSL 510-524 |
| ORR&N 400-405 | 4-6-0 | 5 | Baldwin | 1901 | 1923 (2) | OWRR&N 1729-1732 |
| ORR&N 300-314 | 2-8-0 | 15 | Baldwin | 1901-1903 | 1910-1919 | OWRR&N 710-724 |
| ORR&N 340-344 | 2-8-0 | 5 | Baldwin | 1902 | 1910-1919 | OWRR&N 725-729 |
| UP 1508-1521 | 2-8-0 | 14 | Baldwin | 1902 | 1910-1912 | UP 150-158, OWRR&N 725-729 |
| OSL 800-809 | 4-6-0 | 10 | Baldwin | 1902 | 1906-1909 | OSL 1562-1571 |
| OSL 965-979 | 2-8-0 | 15 | Baldwin | 1903 | OSL 525-539 | |
| UP 1901-1920 | 2-8-0 | 20 | Baldwin | 1903 | UP 480-499 | |
| ORR&N 194-197 | 4-6-2 | 4 | Baldwin | 1905 | 1915-1921 | OWRR&N 3200-3203 |
| UP 21-35 | 4-4-2 | 15 | Baldwin | 1906 | (not rebuilt) | UP 3320-3334 |
Wootten Fireboxes and Camelback Cabs
A Wootten firebox is a type of firebox that was very wide to allow combustion of coal waste, sometimes known as "culm", "boney", or "slack". The low combustibility of the boney coal meant that the fireboxes had to be much wider than a standard firebox. The firebox size meant that the locomotive crew rode the locomotives in camelback cabs mounted across the center of the locomotive boiler. The fireman was exposed to the weather as he fed the fire from the rear deck.
The following is taken from "The Engineer's Encyclopedia" by John G. Winton and William J. Millar, 1890, page cxxx:
The Wootten Firebox - One of the latest novelties in locomotive building has been achieved in rather an indirect manner by Mr. John E. Wootten, formerly Manager of the Philadelphia and Reading Railroad Company. It had occurred to Mr. Wootten that the enormous amount of slack or refuse coal, which is to he found around all coal mines, might possibly be utilized in locomotive fire-boxes, where the opportunity of an enormous draught is possible. He therefore patented a fire-box with a very large surface, indeed, so large that, whereas the fire-box in general use presents a surface of about twenty-six square feet between the wheels, Mr. Wootten, by lifting his fire-box above the wheels, was able to utilize a fire-box with about seventy-five square feet surface. There is a fire-brick arch or division, which is a very essential point in are design of the Wootten fire-box, and gives much of the success of the engines in getting the necessary draught for burning fine coal or slack. Besides the advantage that it gives of utilizing what was formerly worthless waste coal, these engines make steam freely, and haul the heavy express trains of the Union Pacific at a higher rate of speed than has ever before been attained on that road. The coal used is taken from the mines owned by the railroad, and is bituminous, though light, in its character. It is, however, successfully burned without any sparks, a result, of course, due to the enormous grate area, while the heat radiated from the arch fire-bricks or wall maintains an even temperature and insures complete combustion. The large area of the grate prevents any appreciable lifting of the fire, and the small pieces of live coal that are sucked up by the blast are burned on their way to the flues, owing to the high temperature of the brick arch. In the Wootten express engine, of which we give an illustration, it will be seen from the prospective view of the engine and tender, that the engines have two cabs, and thus the fireman is more efficiently sheltered from the weather than is usual on other engines. The severe climate of Nebraska and Wyoming in winter necessitates a very efficient protection for the men working the engines, and the arrangement shown, we are told, is found to answer well. The engine referred to above is one of the large class built by the Rogers Locomotive Works, of Paterson, New Jersey, for the Union Pacific Railway, from the designs of Mr. Clement Hackney, Superintendent of Motive Power of that line.
Union Pacific owned its own coal mines at Rock Springs, and their use of Wootten fireboxes was a move to use the waste coal, or "slack" coal from those mines. After a very brief time, it became apparent that Rock Springs coal and Wootten fireboxes did not mix well and the locomotives were rebuilt to use standard fireboxes and standard cabs.
As noted in the quote above, UP's Wootten 4-4-0s had two cabs. One for the engineer that straddled the boiler, and a partial cab that protected the fireman on the rear deck.
Union Pacific operated eleven 2-8-0 locomotives with Wootten fireboxes and camelback cabs, built by Baldwin in 1886. All 11 were rebuilt in 1893-1895 by UP at Omaha with standard fireboxes and standard cabs.
Union Pacific operated ten 4-4-0 locomotives with Wootten fireboxes and camelback cabs, built by Rogers in 1887. All 10 were rebuilt in 1891-1892 by UP at Omaha with standard fireboxes and standard cabs.
| First Numbers |
Type | Quantity | Builder | Date Built |
Date Rebuilt
To Standard Firebox and Standard Cab |
Later Numbers |
| UPRy 761-770 | 4-4-0 | 10 | Rogers | 1887 | 1891-1892 | UPRy 831-840 in 1891-1892; UP 831-840 in 1898; UP 944, 945 in 1915 |
| UPRy 1301-1311 | 2-8-0 | 11 | Baldwin | 1886 | 1893-1895 | UP 1301-1311 in 1898; UP 100-110 in 1915 |
Belpaire Fireboxes
The Belpaire Firebox had a rectangular cross section and greater volume and heat absorbing area than did a radial stay firebox with the same grate area. Consequently it could produce 10 to 20 percent more steam at the same firing rate. The Pennsylvania had the largest number of such engines, followed by the Canadian National and the Great Northern. (Robert A. LeMassena, 2001)
The Belpaire firebox was invented by Alfred Jules Belpaire in 1860 for the Belgian State Railways to allow use of Belgium's poor grade of coal.
Union Pacific used Belpaire fireboxes on just six 4-6-0s built by Rhode Island for OSL&UN in 1891, and on eight 4-8-0s built by Brooks for UP in 1899. Below are their number series:
| First Numbers |
Type | Quantity | Builder | Date Built |
Later Numbers |
| OSL&UN 1459-1464 | 4-6-0 | 6 | Rhode Island | 1891 | OSL 611-616; OSL 1508-1513 |
| UP 1500-1507 | 4-8-0 | 8 | Brooks | 1899 | UP 1800-1807 |
Wheel Arrangements
Steam locomotives on Union Pacific, like most of America's railroads, used the Whyte classification system for their wheel arrangement, named for Frederick Methvan Whyte.
(click here for more information about the Whyte classification system for steam locomotives)
| 0-6-0 | 2-6-0 | 4-4-0 | 4-6-2 | 4-8-4 | 2-8-8-0 Mallet | 4-6-6-4 |
| 0-8-0 | 2-8-0 | 4-4-2 | 4-8-0 | 4-10-2 | 2-8-8-0 Simple | 4-8-8-4 |
| 2-8-2 | 4-6-0 | 4-8-2 | 4-12-2 | 2-8-8-2 | ||
| 2-10-2 |
UP’s 298 0-6-0 S-Class switchers were built between 1890 and 1921. Road numbers 4226-4246 were LA&SL locomotives and came to UP in 1921. Numbers 4300-4480, along with the 10 USRA locomotives in the 4600-4909 series, were new to UP. Numbers 5700-4763 were OSL locomotives, and numbers 4900-4933 were O-WR&N locomotives.
Retirements for the pre-Harriman era locomotives started as early as 1913. The Harriman era locomotives, built beginning in 1901, were retired starting in 1925 and continued through to 4466’s retirement in 1962.
| S-51 | 4300-4307, 4310-4347, 4700-4702, 4722-4729, 4900-4901, 4931-4933 |
| S-56 | 4226 |
| S-57 | 4227-4228, 4500 |
| S-1 | 4229-4234, 4350-4359, 4730-4734, 4758, 4927-4930 |
| S-2 | 4235-4239, 4360-4400, 4703-4721, 4759-4763, 4902-4922 |
| S-3 | 4240-4242, 4735-4739 |
| S-4 | 4401-4420, 4740-4744, 4923-4926 |
| S-5 | 4421-4450, 4748-4752 |
| S-Spec. | 4600-4609, 4753-4757 |
| S-6 | 4243-4246, 4451-4480 |
| S-57 | UP 4500 |
| M-51 | 4000-4001 |
| M-57 | 4200-4208 |
| M-62 | OSL 4100-4107 |
From 1913 on, UP owned 542 2-8-0s Consolidation-type locomotives. The locomotives were all built between 1888 and 1910, with 19 locomotives, numbers 324-358, coming from the SP in 1910. Beginning with 103 locomotives built in 1901, numbers 401-479, 510-524, and 710-718 series, all 2-8-0 locomotives purchased were built to the Harriman era Common Standard pattern.
The peak years of retirement after 1925 were in 1947, with 92 retired, and again in 1956, with 47 retired.
The last three 2-8-0s on UP were 6264, 6535, and 428. UP 428 was the last operating 2-8-0 and was retired in December 1959. The 6264 and 6535 were the former 264 and 535, renumbered during 1955 and 1956 to avoid conflict with new GP9 diesel units.
These were renumbered at the end of steam into the 6000 series
| C-51 | 100-143, OSL 500-502, 700-706 |
| C-55 | 510-524, 550-554, 707-709 |
| C-57 | 150-158, 402-499, 525-539, 710-729 |
| C-2 | 201-401, 560-622, 730-768 |
2-8-2 (Mikado; after World War II MacArthur or MacA class)
UP’s 362 2-8-2 Mikado (or MacArthur) type locomotives were built between 1910 and 1921, for itself, the OSL, and the LA&SL. The total remained the same until the retirements started in 1946, except for the 2701, which was sold in 1932.
Although the total quantities didn't change, there had been some swapping between UP and its subsidiaries. In 1918 OSL sent seven locomotives to the LA&SL. In 1920 UP renumbered its USRA series. In 1923 UP sent 18 2-8-2s to the OSL, OSL sent 10 locomotives to the UP, and LA&SL sent 10 2-8-2s to the OSL.
| MK-1 | 1900-1929, 2000-2014, 2100-2140 |
| MK-2 | 1930-1949, 2015-2034, 2141-2165 |
| MK-8 | 2166-2171 |
| MK-3 | 2200-2209 |
| MK-4 | 2210-2219, |
| MK-5 | 2220-2244, 2500-2514, 2726-2732 |
| MK-6 | 2245-2259, 2700-2708 |
| MK-7 | 2260-2279, 2515-2514, 2709-2715, 2733-2735 |
| MK-8 | 2280-2294, 2311-2320, 2525-2534 |
| MK-Spec. | 2295-2314, 2535-2554 |
| MK-9 | 2295-2310 |
| MK-10 | 2555-2564, 2716-2725 |
| TTT-1 | 5000-5009, 5525 |
| TTT-2 | 5300-5305 |
| TTT-3 | 5010-5014, 5526-5529 |
| TTT-4 | 5015-5039 |
| TTT-5 | 5314-5415 |
| TTT-6 | 5040-5089, 5306-5313, 5500-5514 |
| TTT-7 | 5515-5524 |
From 1916 on, UP owned 88 4-4-0 American-type locomotives. All were retired by 1936, with only a single locomotive on the roster between 1933 and the final year of 1936.
| E-56 | 1056-1057 |
| E-57 | 1111 |
| E-61 | 1000-1001 |
| E-62 | 900-930, 1002, 1004-1013, 1052-1055, 1122-1123 |
| E-63 | 1003, 1102-1108 |
| E-64 | 1114-1121 |
| E-69 | 931-851, 450, 1058-1061 |
| E-70 | 1050 |
UP’s 66 4-4-2 Atlantic type locomotives were built between 1903 and 1911. All were retired by the end of 1933. The first group of 4-4-2s to be retired were the 14 Baldwin Vauclain compounds, retired in 1921, with the last two retired in 1923.
UP had 35 locomotives, OSL had 12, LA&SL had 4, and OWRR&N had 15.
| A-2 | 3300-3319, 3400-3411 |
| A-3 | 3320-3334 |
| A-1 | 3376-3379 |
| A-4 | 3500-3514 |
From 1915 on, UP owned a total of 306 4-6-0 Ten-Wheelers. Most were retired by 1946, with one still on the roster. UP 1243 was retained after the second to last Ten-Wheeler was retired in 1955, and is preserved as part of the railroad’s Historical Collection at Cheyenne, Wyoming.
Four 4-6-0s (UP 1584-1587) were acquired by UP from its former subsidiary, Pacific and Idaho Northern, in 1936.
| T-1 | 1755-1760 |
| T-2 | 1572-1578, 1742-1747 |
| T-3 | 1579-1583, 1748-1754 |
| T-51 | 1514-1529 |
| T-54 | 1502 |
| T-55 | 1701-1708 |
| T-57 | 1200-1216, 1222-1225, 1227-1230, 1233-1236, 1239-1247, 1306, 1500-1501, 1540-1561, 1584, 1586-1587, 1733-1741 |
| T-61 | 1250-1289, 1585 |
| T-62 | 1226, 1311, 1319, 1503-1513 |
| T-63 | 1360-1369, 1709-1726 |
| T-64 | 1727-1732 |
| T-68 | 1591-1596 |
| T-69 | 1220-1221, 1231-1232, 1238, 1300-1305, 1307-1310, 1312-1318, 1320-1329, 1534-1539 |
| T-73 | 1330-1347, 1562-1571 |
| T-79 | 1348-1359 |
UP’s 209 4-6-2 Pacific type locomotives were built between 1903 and 1920. The retirements began as early as 1926 and continued through 1958. UP 3203 was the last 4-6-2 on the railroad. The worst years for retirements were in 1933 (22 retired), 1934 (15 retired) and 1947 (59 retired).
In 1928, two OSL 3100s were transferred to UP 2900s.
| P-1 | 2800-2818, 3150-3170, 3204-3207 |
| P-2 | 3200-3203 |
| P-3 | 2819-2824, 3100-3103, 3208-3210 |
| P-4 | 2825-2828, 3173-3175 |
| P-5 | 2829-2848 |
| P-6 | 2850-2859, 3104-3113, 3211-3217 |
| P-7 | 3218-3219 |
| P-8 | 2860-2869, 3114-3123, 3176-3181 |
| P-9 | 2870-2879, 3124-3128 |
| P-10 | 2880-2899, 2910, 3129-3133 |
| P-11 | 3134-3138 |
| P-12 | 3226-3227 |
| P-13 | 2900-2909, 2911 |
From 1915 on, UP owned 15 4-8-0 Twelve-Wheelers. The first five were retired in 1925 and the final locomotives were retired in 1928.
| TW-57 | 1800-1807 |
| TW-55 | 1850-1856 |
| MT-1 | 7000-7039, 7850-7864 |
| MT-2 | 7865-7869 |
The 45 FEF (Four-Eight-Four) class locomotives were in three classes. The 20 FEF-1, numbers 800-819, were delivered in 1937. The 15 FEF-2 locomotives, numbers 820-834, were delivered in 1939, and the final 10 FEF-3 locomotives, numbers 835-844, were delivered in 1944, and were the last steam locomotives built new for UP.
| FEF-1 | 800-819 |
| FEF-2 | 820-834 |
| FEF-3 | 835-844 |
| FTT-1 | 8000 |
| FTT-2 | 8800-8808 |
| UP-1 | 9000 |
| UP-2 | 9001-9014, 9708 |
| UP-3 | 9015-9029, 9700-9707 |
| UP-4 | 9030-9054 |
| UP-3 | 9055-9062 |
| UP-5 | 9063-9087, 9500-9514 |
UP’s 70 2-8-8-0 Articulated Consolidations were all built between 1918 and 1924 as Mallet Compound, CS Class MC, locomotives. In 1936 the locomotives were rebuilt from compound to simple, with a change in class, from CS Class MC to CS Class SA-C (for Simple Articulated Compound). beginning in 1937, as the rebuilding was completed, they were renumbered from the 3600 class to the 3500 class. The two OSL 3700 class and three OSL 3800 class locomotives were also rebuilt to simple locomotives, but retained their original numbers until 1944 when they were renumbered to the 3500 series to vacate the two number series to make way for the 4-6-6-4 locomotives.
Retirements began in 1947 and continued through 1954.
| MC-2 | 3600-3614, 3644, 3703, 3800-3802 |
| MC-3 | 3615-3633 |
| MC-4 | 3634-3638, 3704-3705, 3803-3805 |
| MC-5 | 3639-3643 |
| MC-6 | 3645-3664 |
| Class | Built | UP | OSL | OWRR&N | LA&SL |
| MC 2 | 1918 | UP 3600-3614 | OSL 3703 | ||
| MC 3 | 1920 | UP 3615-3633 | |||
| MC 4 | 1922 | UP 3634-3638 | OSL 3704, 3705* | OWRR&N 3803-3805* | |
| MC 5 | 1923 | UP 3639-3643 | |||
| MC 6 | 1924 | UP 3645-3664 |
2-8-8-0 (Simple Articulated - Consolidation)
| SA-C-2 | 3500-3514 (after Atlantics Scrapped) |
| SA-C-3 | 3515-3533, 3544, 3565-3569 |
| SA-C-4 | 3524-3538 |
| SA-C-5 | 3539-3543 |
| SA-C-6 | 3545-3564 |
2-8-8-2 (Simple Articulated and Mallet Compounds)
| SA-57 | 3570-3588 (ex C&O H-7) |
| SA-57 | 3589-3599 (ex C&O H-7a) |
| MC-57 | 3670-3674 (ex N&W Y-3) |
4-6-6-4 (Challenger Simple Articulated)
| CSA-1 | 3801-3814; renumbered from 3900 class |
| CSA-2 | 3815-3839; renumbered from 3900 class |
| 4664-5 | 3930-3949 |
| 4664-3 | 3950-3969 |
| 4664-4 | 3969-3999 |
| 4884-1 | 4000-4019 |
| 4884-2 | 4020-4024 |
Tractive Force and Horsepower
From The Streamliner, Volume 2, Number 4, page 28
Formula for converting tractive force to horsepower at the rails (both steam and diesel locomotives).
(tractive force in pounds) x (speed in miles per hour) / 375 = (horsepower at the rails)
(drawbar pull in pounds) x (speed in miles per hour) / 375 = (drawbar horsepower)
(tractive force in pounds) x (speed in feet per minute) / 33000 = (horsepower)
For steam locomotives:
(0.85 boiler pressure in pounds) x (cylinder diameter in inches, squared) x (stroke in inches) / (driver diameter in inches) = (tractive force in pounds)
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