Milwaukee Road 4-8-4 "Northern" Type Locomotives


The Chicago, Milwaukee, St. Paul & Pacific Railroad's own motive power department designed a Class S-1, 4-8-4 in 1930. It was built by the Baldwin Locomotive Works and put on the roster as number 9700. It remained the lone Northern on the CMStP&P for the next seven years. A second one-of-a-kind was built in 1938 in CMStP&P's own shops in Milwaukee, WI. This was also a Class S-1 and was given road number 251. At this time number 9700 was renumbered 250.

In 1937, an order of 30 Class S-2s was delivered from Baldwin. These were given road numbers 201 through 230. A second order of 10 Class S-2s were delivered from Baldwin in 1940 (road numbers 231 through 240). The Class S-2 Northerns weighed 490,450 lbs, had 74" drivers, 26 x 32 cylinders, 285 lbs psi and had a tractive effort of 70,800 lbs.

Because of wartime needs, another order of 10 (road numbers 260 through 269) Class S-3 Northerns was delivered in 1943 from the American Locomotive Company. This class was designed to have 74" drivers, 26 x 32 cylinders, 250 lbs psi boiler pressure and weighed 460,000 lbs and had a tractive effort of 62,040 pounds.

There are two survivors: number 261, which is operational and number 265 at the Illinois Railway Museum in Union, IL. When 261 is not running, it is stored at the old GN Shops near Minneapolis Junction in Minneapolis, MN.

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder
S-1250 (ex 9700)1930Baldwin

Class Details by Steve Llanso

Class S1 (Locobase 247)

Data from 1930 Locomotive Cyclopedia tables and DeGolyer, Volume 82, pp. 246+. Also see Steve Glischinski's article on the MIlwaukee's generations of 4-8-4s at, last accessed 23 September 2007.

As with most Class 1 locomotives built in this period, the firebox's heating surface area included a variety of structures and supplements. The combustion chamber contributed 122 sq ft (11.3 sq m), NIcholson thermic syphons (two in the firebox, one in the combustion chamber) 116.5 sq ft (10.8 sq m) and arch tubes 16.5 sq ft (1.5 sq m). The boiler's Coffin feedwater heater was to be "applied in recess provided in smoke box.". In addition, the firebox was fitted with a "smoke consuming device".

The 14" piston valves had 9" of travel.

This was the proof-of-concept Northern for the Milwaukee Road. Glischinski's account says that 9700 (works number was 61176 in December 1929) entered service in 1930 from Baldwin as a trial horse against the powerful F6 4-6-4s then in service. He contends that the S1 was a stretched F6 in any case. Baldwin called it a "Modified Mountain".

For the moment, the Milwaukee's passenger trains made do with the F6 and the 9700 was put to work pulling 5,000-ton freights on its own. In 1934, the 9700 began working passenger trains between Avery, Idaho and Othello, Washington. In February 1938, the West Milwaukee shops duplicated the 9700, by then renumbered 250, and rolled out the 251. (Glischinski notes that it was the last new locomotive from that facility.)

Class S2 - circulator (Locobase 248)

Data from 1947 Locomotive Cyclopedia table and diagram and from MILWRD 1945 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. (Thanks to Chris Hohl for a correction of the boiler pressure.) Works numbers were 62092 in October 1937 and 62344, 62346 in March 1940; 62345, 62347 in April; 62348-62353 in May.

Engines 203 and 231-240 used 105.5 sq ft (9.8 sq m) of circulators to supplement firebox heating surface instead of the 147 sq ft (13.65 sq m) of thermic syphons installed in the rest. See the photo provided on 16 September 2008 by "Mark D" to the Chaski Forum; it illustrates splendidly the arrangement of the tubes and the firebricks that lay on top of them. The firebox also had a combustion chamber.

These forty S-2s operated mostly as freight haulers from Bensenville to Council Bluffs, Iowa or St. Paul, Minn. Occasionally they'd hook up to the westbound Olympian if it trailed more than twelve cars.

Retired 1953-1956.

Class S2 - thermic syphon (Locobase 11085)

Data from MILWRD 1945 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.. See also "New Power for the MIlwaukee Road", Baldwin Locomotives Magazine, pp. 1-5, archived at, last accessed 10 August 2014. Works numbers were works numbers 62089-62091 in October 1937, 62093-62095 in November, 62096-62102 in December, 62103-62110 in January, 62111-62116 in February, and 62117 in March.

Even before theWest Milwaukee shops produced the 251 (see Locobase 247), the Milwaukee Road had gone to Baldwin for its definitive Northerns. The first 28 were produced in October 1937 through February 1938

147 sq ft (13.66 sq m) of thermic syphons contributed to the firebox heating surface as did the combustion chamber. They had 14" (356 mm) piston valves with 7 1/2" (191 mm) of travel. Their backbones were one-piece cast steel beds from General Steel Castings Corporation. Boxpok drivers turned on Timken roller bearings, as did the front truck's wheels; rear truck and tender wheels used American Steel Foundries roller bearings.

Engines 203 and 231-240 used 105 sq ft (9.75 sq m) of circulators to supplement firebox heating surface; see Locobase 248 for the data.

These S-2s operated mostly as freight haulers from Bensenville (West Milwaukee) to Council Bluffs, Iowa or St. Paul, Minn. Occasionally they'd hook up to the westbound Olympian if it trailed more than twelve cars.

Retired 1953-1956.

Class S3 (Locobase 249)

Data from 1947 Locomotive Cyclopedia tables. Also see Steve Glischinski's article on the MIlwaukee's generations of 4-8-4s at, last accessed 23 September 2007. Works numbers were 71973-71979 in July 1944, 71980-71982 in September.

Firebox heating surface included 80.5 sq ft (7.48 sq m) of circulators.

The last of the Milwaukee Road's Northerns, this design pieced together a Rock Island frame, a Delaware & Hudson boiler, and a Union Pacific tender. Like the 1940 batch from Baldwin, the boiler used circulators in place of thermic syphons. Glischinski's account says of this batch " Alco ad touted them as 'the last word in 4-8-4 design.' They featured roller bearings, special compensating lateral driving-box devices, and precision firing equipment."

Four were later converted to oil-burning and the engines saw out steam in both freight and passenger service with retirements coming in 1954-1956.

Specifications by Steve Llanso
ClassS1S2 - circulatorS2 - thermic syphonS3
Locobase ID247 248 11085 249
RailroadMilwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)
Road Numbers9700/250203, 231-240201-202, 204-230260-269
Valve GearBakerWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase19.75'19.25'19.25'19.75'
Engine Wheelbase46.25'47.33'47.33'46.59'
Ratio of driving wheelbase to overall engine wheebase 0.43 0.41 0.41 0.42
Overall Wheelbase (engine & tender)88.33'92.04'96.04'95.50'
Axle Loading (Maximum Weight per Axle)65136 lbs
Weight on Drivers258818 lbs282320 lbs282320 lbs259300 lbs
Engine Weight450840 lbs490450 lbs490450 lbs460000 lbs
Tender Light Weight289169 lbs323000 lbs397000 lbs364100 lbs
Total Engine and Tender Weight740009 lbs813450 lbs887450 lbs824100 lbs
Tender Water Capacity15000 gals20000 gals20000 gals25000 gals
Tender Fuel Capacity (oil/coal)20 tons25 tons25 tons20 tons
Minimum weight of rail (calculated) on which locomotive could run108 lb/yard118 lb/yard118 lb/yard108 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter74"74"74"74"
Boiler Pressure230 psi285 psi285 psi250 psi
Cylinders (dia x stroke)28" x 30"26" x 32"26" x 32"26" x 32"
Tractive Effort62137 lbs70816 lbs70816 lbs62119 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.17 3.99 3.99 4.17
Heating Ability
Firebox Area549 sq. ft536 sq. ft578 sq. ft505.50 sq. ft
Grate Area103 sq. ft106 sq. ft106 sq. ft96.20 sq. ft
Evaporative Heating Surface5400 sq. ft5468 sq. ft5509 sq. ft4478 sq. ft
Superheating Surface2403 sq. ft2336 sq. ft2336 sq. ft1438 sq. ft
Combined Heating Surface7803 sq. ft7804 sq. ft7845 sq. ft5916 sq. ft
Evaporative Heating Surface/Cylinder Volume252.57278.07280.16227.73
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation23690302103021024050
Same as above plus superheater percentage31034392733927329822
Same as above but substitute firebox area for grate area165414198588214149156705
Power L139501521465259431278
Power MT1345.881628.821642.811063.73




Introduction and roster provided by Richard Duley. Class details and specifications provided by Steve Llanso of Sweat House Media.