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 tht e 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.

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 collection.

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 locomotive 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 result was a considerably heavier, but more powerful Atlantic that remained in service as a single-engine class until 1951.

Class A1 (Locobase 385)

Data from American Engineer & Railroad Journal (AERJ) for February 1896. Works number 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. 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 writing, 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. 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. Like the later Milwaukee Road As, these operated as compounds until their retirement in the late 1920s.

Class A2a (Locobase 10787)

Data from Baldwin Locomotive Works, Record of Recent Construction ((1903), No. 39, p.2626-263 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. This subclass apparently never was modified for simple expansion and all were scrapped in the late 1920s.

Class A2c (Locobase 2784)

Data from Milwaukee Road 1930 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive collection. 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. Jim Scribbins (in Drury, 1993) says these engines followed 5 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.