Idaho & Washington Northern / Milwaukee Road 4-4-2 "Atlantic" Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class 31 (Locobase 11454)

Data from "Baldwin 4-4-2 for the Idaho & Washington Northern" Railway and Locomotive Engineering, Vol 23, No 2 (February 1910), pp. 52-53. Works number was 33778 in September 1909.

This single Atlantic was equipped with a Baldwin smokebox superheater. According to the RLE report, the exhaust gases traveling down the tubes first hit a deflecting plate: "The deflecting plate is cylindrical in form, with a conical extension at the rear. It is centrally placed in a horizontal position, between the right and left hand sections of the superheater. The space enclosed by the deflecting plate can be entered at the front end only and is in direct communication with the stack by means of a downward extension of the latter."

The purpose of this arrangement was to ensure "...[t]he hot gases are thus compelled to traverse the entire length of the smokebox, during which time they circulate among the superheater tubes. The exhaust pipe is extended upward to the deflecting plate and has a single nozzle"

So obviously as much heat as was possible was meant to transfer from the gases to the superheater elements. Designers soon found that the Schmidt firetube superheater was much more effective and smokebox superheaters soon faded out of use. Note how low the boiler pressure was.

When the Milwaukee took over the I & WN in 1916, they placed this locomotive in its own A-2/3s class. In the 1930s, the 3135 was later considerably modified with a Schmidt superheater; see Locobase 11455.


Class A (Locobase 106)

Data from 1947 Locomotive Cyclopedia table. (Many thanks to Chris Hohl for his 22 September 2017 email reporting unlikely boiler pressure values for 177 entries. A Locobase macro caused the error .)

Firebox fitted with 40 sq ft of thermic syphons and arch tubes. Among the last 4-4-2s to be built, the engine had high drivers and a brightly colored, air-smoothed casing. Although seemingly lightweight, the four oil-fired engines developed over 3,000 cylinder horsepower and kept a 6 1/4 hour schedule over the 408-mile run between Chicago and Minneapolis with 9 cars.

Alfred Bruce (The Steam Locomotive in America, 1952, 292-293) proudly describes the performance of this Alco product, for whose design he may well have shared responsibility: "Their ample boiler capacity, 19 x 28 cylinders, 84" drivers, and 300 psi made them about the highest-speed steam locomotive engines ever constructed. During the time-schedule stabilizing runs, the hand of the speed indicator was often reported against the pin at 128 miles per hour. Exactly what maximum speed was reached is not known - but it was plenty!" [Locobase observes that 128 is two miles per hour faster than the 126 mph the LNER's Mallard (Locobase 1066) achieved in 1937 for the highest officially recognized speed posted by a steam locomotive.]

Bruce gives further details about the design: "The Hiawatha engines had their main rods connected to the front axle and were remarkably stable riding." He adds that this quartet were among the first to press a conventionally staybolted boiler to 300 psi. He also notes that the streamlining fairing proved very effective in protecting the crew and the train from wandering livestock. One of the four, traveling at 100 mph, hit a cow and sent it "sailing out over the telephone wires along one side of the right of way." All of the cow's bones were broken, he observes, but the hide was intact.


Class A-4s/B-4s (Locobase 11455)

Data from MILWRD 1945 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Superheater area is an estimate based on several similar classes, especially that of the Chicago & Alton E-1 (Locobase 9040), which also had a very similar boiler and grate. At some point, the Milwaukee decided to remove the Baldwin smokebox superheater that had accompanied the 3135 when it was delivered to the Idaho & Northern Washingtion in 1909 (Locobase 11454). At the same time the shops mounted a new boiler, they also rolled in taller drivers.

The shops also took the opportunity to take the two balanced-compound A2s shown in Locobase 13053, modify them to hold superheaters, and put on smaller drivers.

The result was considerably heavier, but more powerful Atlantics that remained in service until 1951. In fact, the last steam passenger train on the Milwaukee made its final run behind one of the two balanced-compound engines.


Class A-4s/B-4s (Locobase 13054)

Data from MILWRD 1945 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange.

Superheater area is an estimate based on several similar classes, especially that of the Chicago & Alton E-1 (Locobase 9040), which also had a very similar boiler and grate. When the shops simpled, superheated, and otherwise overhauled the lone balanced compound from the Idaho & Washington, they also took the opportunity to take the two balanced-compound A2s shown in Locobase 13053, modify them to hold superheaters, and put on smaller drivers. Another difference was the smaller number of 2" tubes fitted in the Milwaukee Road engines.

The result was considerably heavier, but more powerful Atlantics that remained in service until 1951. In fact, the last steam passenger train on the Milwaukee made its final run behind one of the two balanced-compound engines.


Class A1 (Locobase 385)

Data from American Engineer & Railroad Journal (AERJ) for February 1896. works numbers were 14861-14862. Additional batches of the same design comprised works numbers 15462-15463 in August 1897, 16315-16319 November 1898, and 17222-17225 in November 1899, and, surprisingly, 22708, 22732, 22751-22752, and 22811 (road numbers 941-945), which were produced in August 1903 and only differed in having 7,000-gallon tenders and 2 fewer tubes.

Used same cylinder dimensions as Baldwin's earlier 2-4-2 Columbia, but with a bigger boiler on the 4-4-2 arrangement. AERJ showed the long-striding Atlantic and comments that it was intended for the express service between Chicago & Milwaukee. (See DeGolyer , volume 20, p. 140, attachment, for the details of the guarantee demanded by the Milwaukee.)

While an hour & a half for the 85 miles may not seem so impressive, the author observes, the locomotives would be hauling 10 heavyweight cars. Moreover, taking account of the 10-minute timing for the first 4 congested miles shows that the other 81 would be covered in about 80 minutes.

At the time of that report, these 4-cylinder Vauclain compounds had just entered service. The writer noted one run in which 839 pulled 14 cars of well over 500 tons on a schedule of 1 hour 55 minutes with 2 intermediate stops and a delay of 5 minutes. It reeled off 80 mph for several consecutive miles.

Once completed in 1899, the class was renumbered twice, once in 1901 to 900-912 and again in 1912 to 3000-3017. In later years, some, but not all, were rebuilt as 2-cylinder, simple-expansion engines. 3000-3001 were given 20" x 26 cylinders and 3002, 3005, 3007-3011, 3013, and 3015 took on 19" x 26" cylinders.


Class A2 (Locobase 4119)

Data from 20 September 1901 Railroad Gazette and from Baldwin Locomotive Works, Record of Recent Construction ((1903), No. 35, p. 7. See also DeGolyer, Volume 24, p. 100 Works numbers were 19655-19663.

These were the first of the "all-outside" Vauclain compound Atlantics on the CM&St P. (The Vauclain setup had one HP & one LP cylinder on each side driving off the same crosshead.) The single piston valve that served both cylinders on each side measured 15" (381 mm) in diameter, which was about as large as these valves would get. "Not to Exceed" weight estimates turned out to be five short tons (4.54 tonnes) too low.

Like the later Milwaukee Road A2s (Locobase 10787), these operated as compounds until their retirement in the late 1920s.


Class A2 - balanced compound (Locobase 13053)

Data from Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University Volume 30, p. 72. See also "Balanced Compound Atlantic Locomotive for the Chicago, Milwaukee & St. Paul," The Railroad Gazette Volume XLIII, No. 20 (15 November 1907), pp 596-597. Works numbers were 31274-31275 in July 1907.

Among the Vauclain compounds delivered before and after the 951-952, the two balancend compounds had all four cylinders driving on the front axle and also had larger 2 1/4" tubes than the others. Firebox heating surface included 28 sq ft of arch tubes. They used the trailing truck designed by the Milwaukee's own DeVoy.

Remarkably, the pair remained compounds for more than 30 years. In 1938, they were converted to A-4a simple-expansion engines with two 22" x 28" cylinders driving on the second axle and 79" drivers; see Locobase


Class A2a (Locobase 10787)

Data from Baldwin Locomotive Works, Record of Recent Construction ((1903), No. 39, p.262-263. See also DeGolyer, Volume 25, pp. 20+. Works numbers were 21034-21035, 21080-21081, 21105-21106, 21119-21120, 21138-21139, 21158-21159, 21201-21203..

Following immediately after the first A2s (Locobase 4119), this class saw very few changes in the design. Like the others, this class had one 15" (381 mm) balanced piston valve to serve each set of 1 HP and 1 LP cylinder. One small modification involve moving the driving box equalizers. In previous engines, says a note in the specs, the equalizers made it "impossible to renew waste [to hold lubricant] on top of driving box and to properly oil."

This subclass apparently never was modified for simple expansion and all were scrapped in the late 1920s.


Class A2c (Locobase 2784)

Data from DeGolyer, Volume 32, pp. 19+. See also American Engineer and Railroad Journal, Volume 83, No.3 (March 1909), p. 115; "Western Railway Club", Engineering, Volume LV [55], No. 17 (26 April 1906); and Milwaukee Road 1930 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. Baldwin works numbers were 33091-33093 in December 1908; 33110-33112, 33119-33124 in January 1908.

OS Nock (RWC IV, pl 2) notes that these were the last Atlantics to be procured by the Milwaukee Road. They were "all-outside" and used the Vauclain compounding system of HP & LP cylinders driving off the same crosshead. Each set of LP/HP cylinders were supplied by a single 15" (381 mm) piston valve set inside and operated by a rocker from the outside valve gear's combination lever.

Their DeVoy design trailing trucks had inside journals whose boxes were part of a single casting. The boxes at each end of the beam were guided by cast steel pedestals and the assembly, which required no radius bar, had 2 1/2" (63.5 mm) of lateral play.

At a time (early 1906) when many railroads had begun to convert most of their compounds to simple-expansion. J H DeVoy, then Mechanical Engineer of the Milwaukee Road, contested a claim during a 17 April 1906 meeting of the Western Railway Club that the amount of work in the HP and LP cylinders in a Vauclain compound locomotive was "so unequal as to set up great strains in the crosshead and guides and to cause dangerous pounding." DeVoy acknowledged that this might sometimes be the case, but that the problem could be "easily avoided by proper design, and is no argument against the compound principle."

A E Manchester, of the same railroad, reported that the Milwaukee Road then operated 250 compounds and expected to order more. He nevertheless tempered his support by observing that they showed "higher economy in fuel consumption on divisions where trains are slow and heavy than where a fast schedule and lighter trains are the rule."

Jim Scribbins (in Drury, 1993) says these engines followed five very similar A2b engines produced by the railroad.

All 17 retired in 1927-1930 without being converted to simple-expansion.

Both Nock and Scribbins give the tractive effort as 22,200 lb, while the figure in the specifications is derived through the 1924 ARA formula. In any case, note the relatively high LP/HP ratio, which suggests that the LP cylinders ran out of steam at late cutoffs.

Principal Dimensions by Steve Llanso of Sweat House Media
Class31AA-4s/B-4sA-4s/B-4sA1
Locobase ID11,454 106 11,455 13,054 385
RailroadIdaho & Washington Northern (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)
CountryUSAUSAUSAUSAUSA
Whyte4-4-24-4-24-4-24-4-24-4-2
Number in Class141222
Road Numbers31 / 3512/3135/323506-35093135 / 3230-31838-841, 871-875, 941-945 / 400-412
GaugeStdStdStdStdStd
Number Built1422
BuilderBaldwinAlco-SchenectadyMilwaukeeMilwaukeeBurnham, Williams & Co
Year19091935193819381896
Valve GearWalschaertWalschaertWalschaertWalschaertStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m)7 / 2.13 8.50 / 2.59 7.33 / 2.23 7.33 / 2.23 6.75 / 2.06
Engine Wheelbase (ft / m)27 / 8.2337.60 / 11.4629.21 / 8.9029.21 / 8.9025.50 / 7.77
Ratio of driving wheelbase to overall engine wheebase 0.26 0.23 0.25 0.25 0.26
Overall Wheelbase (engine & tender) (ft / m)57.60 / 17.5679 / 24.0862.35 / 1950 / 15.24
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)101,600 / 46,085142,000 / 64,410122,900 / 55,747121,540 / 55,13071,600 / 32,477
Engine Weight (lbs / kg)196,900 / 89,312286,000 / 129,728216,000 / 97,976208,800 / 94,710140,700 / 63,821
Tender Loaded Weight (lbs / kg)138,100 / 62,641219,620 / 99,618143,680 / 65,172134,000 / 60,781103,000 / 46,720
Total Engine and Tender Weight (lbs / kg)335,000 / 151,953505,620 / 229,346359,680 / 163,148342,800 / 155,491243,700 / 110,541
Tender Water Capacity (gals / ML)7000 / 26.5213,000 / 49.247000 / 26.527000 / 26.524500 / 17.05
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)12 / 10.904000 / 15.2010 / 9.1010 / 9.10
Minimum weight of rail (calculated) (lb/yd / kg/m)85 / 42.50118 / 59102 / 51101 / 50.5060 / 30
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)73 / 185484 / 213479 / 200779 / 200778 / 1981
Boiler Pressure (psi / kPa)160 / 11300 / 20.70200 / 13.80200 / 13.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)22" x 28" / 559x71119" x 28" / 483x71122" x 28" / 559x71122" x 28" / 559x71113" x 26" / 330x660
Low Pressure Cylinders (dia x stroke) (in / mm)22" x 26" / 559x660
Tractive Effort (lbs / kg)25,248 / 11452.3130,685 / 13918.5029,163 / 13228.1329,163 / 13228.1314,196 / 6439.20
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.02 4.63 4.21 4.17 5.04
Heating Ability
Firebox Area (sq ft / m2)189 / 17.57294 / 27.32172 / 15.99168 / 15.61171 / 15.89
Grate Area (sq ft / m2)49.80 / 4.6369 / 6.4149.80 / 4.6349.80 / 4.6330.20 / 2.81
Evaporative Heating Surface (sq ft / m2)3163 / 293.963245 / 301.582223 / 206.602084 / 193.682245 / 208.64
Superheating Surface (sq ft / m2)367 / 34.111029 / 95.63507 / 47.12507 / 47.12
Combined Heating Surface (sq ft / m2)3530 / 328.074274 / 397.212730 / 253.722591 / 240.802245 / 208.64
Evaporative Heating Surface/Cylinder Volume256.76353.16180.45169.17562.06
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation796820,700996099606040
Same as above plus superheater percentage876525,66811,85211,9526040
Same as above but substitute firebox area for grate area33,264109,36840,93640,32034,200
Power L111,71163,88416,34416,0047046
Power MT508.231983.66586.37580.59433.90

Principal Dimensions by Steve Llanso of Sweat House Media
ClassA2A2 - balanced compoundA2aA2c
Locobase ID4119 13,053 10,787 2784
RailroadMilwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)Milwaukee Road (CMStP&P)
CountryUSAUSAUSAUSA
Whyte4-4-24-4-24-4-24-4-2
Number in Class2821512
Road Numbers913-921/3100-3108951-952 / 3133-3134922-936/3109-31233500-3511
GaugeStdStdStdStd
Number Built2821512
BuilderBurnham, Williams & CoBurnham, Williams & CoBurnham, Williams & CoBurnham, Williams & Co
Year1901190719021908
Valve GearStephensonStephensonStephensonWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m) 7.25 / 2.21 7.50 / 2.29 7.25 / 2.21 7.33 / 2.23
Engine Wheelbase (ft / m)27.96 / 8.5232.17 / 9.8127.96 / 8.5229.21 / 8.90
Ratio of driving wheelbase to overall engine wheebase 0.26 0.23 0.26 0.25
Overall Wheelbase (engine & tender) (ft / m)68.59 / 20.9153.35 / 16.2656.46 / 17.2161.08 / 18.62
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)100,335 / 45,511106,000 / 48,08192,450 / 41,935108,750 / 49,328
Engine Weight (lbs / kg)181,535 / 82,343195,000 / 88,451177,470 / 80,499210,400 / 95,436
Tender Loaded Weight (lbs / kg)139,465 / 63,260134,000 / 60,781132,530 / 60,115132,600 / 60,146
Total Engine and Tender Weight (lbs / kg)321,000 / 145,603329,000 / 149,232310,000 / 140,614343,000 / 155,582
Tender Water Capacity (gals / ML)7000 / 26.527000 / 26.527000 / 26.527000 / 26.52
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)9 / 8.2010 / 9.109 / 8.2010 / 9.10
Minimum weight of rail (calculated) (lb/yd / kg/m)84 / 4288 / 4477 / 38.5091 / 45.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)84 / 213485 / 215984.25 / 214185 / 2159
Boiler Pressure (psi / kPa)200 / 13.80220 / 15.20200 / 13.80220 / 15.20
High Pressure Cylinders (dia x stroke) (in / mm)15" x 28" / 381x71115" x 28" / 381x71115" x 28" / 381x71115" x 28" / 381x711
Low Pressure Cylinders (dia x stroke) (in / mm)25" x 28" / 635x71125" x 28" / 635x71125" x 28" / 635x71125" x 28" / 635x711
Tractive Effort (lbs / kg)18,750 / 8504.8720,382 / 9245.1318,694 / 8479.4720,382 / 9245.13
Factor of Adhesion (Weight on Drivers/Tractive Effort) 5.35 5.20 4.95 5.34
Heating Ability
Firebox Area (sq ft / m2)183.30 / 17.03183 / 17.01173.30 / 16.11214.30 / 17.26
Grate Area (sq ft / m2)46.71 / 4.3445.80 / 4.2646.71 / 4.3445 / 4.18
Evaporative Heating Surface (sq ft / m2)3192 / 296.543198 / 297.213182 / 295.723188 / 293.57
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)3192 / 296.543198 / 297.213182 / 295.723188 / 293.57
Evaporative Heating Surface/Cylinder Volume557.37558.42555.63556.67
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation934210,07693429900
Same as above plus superheater percentage934210,07693429900
Same as above but substitute firebox area for grate area36,66040,26034,66047,146
Power L17231805871478345
Power MT317.77335.19340.86338.35

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