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, 1950, 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 A1 (Locobase 385)

Used same cylinder dimensions as Baldwin's earlier 2-4-2 Columbia, but with a bigger boiler on the 4-4-2 arrangement. American Engineer & Railroad Journal (AERJ) for February 1896 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.

Class A2 (Locobase 4119)

Profiled in the 20 September 1901 Railroad Gazette, 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 A2c (Locobase 2784)

Data from Milwaukee Road 1930 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

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.

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.