Milwaukee Road class A

The Milwaukee Road class "A" was a class of high-speed, streamlined 4-4-2 "Atlantic" type steam locomotives built by the American Locomotive Company (ALCO) from 1935 to 1937 to haul the Milwaukee Road's Hiawatha express passenger trains. Numbered from No. 1 to No. 4, they were among the last Atlantic type locomotives built in the United States, and certainly the largest and most powerful. The class were the first locomotives in the world built for daily operation at over 100 mph (160 km/h), and the first class built completely streamlined, bearing their casings their entire lives. Although partially supplanted by the larger class "F7" Hudsons from 1937, they remained in top-flight service until the end. Locomotive No. 3 was taken out of service in 1949 and cannibalized for spare parts to keep the other three running until 1951.

Milwaukee Road class A
Hiawatha Milwaukee Road Postkarte 1935.jpg
A postcard depicts the Milwaukee Road class A #2 in 1935.
Type and origin
BuilderAmerican Locomotive Company
Serial number68684 (1), 68685 (2), 68729 (3), 68828 (4)
Build dateMay 1935 (2), May 1936, April 1937
Total produced4
 • Whyte4-4-2
 • UIC2′B1′ h2
Gauge4 ft 8+12 in (1,435 mm) standard gauge
Driver dia.84 in (2,134 mm)
Length88 ft 8 in (27.03 m)
Adhesive weight144,500 lb (65,500 kilograms; 65.5 metric tons)
Total weight537,000 lb (244,000 kilograms; 244 metric tons)
Fuel typeOil
Fuel capacity4,000 US gal (15,000 l; 3,300 imp gal)
Water cap.13,000 US gal (49,000 l; 11,000 imp gal)
Boiler pressure300 psi (2.07 MPa)
Heating surface3,245 sq ft (301.5 m2)
 • Firebox69 sq ft (6.4 m2)
 • Heating area1,029 sq ft (95.6 m2)
Cylinder size19 in × 28 in (483 mm × 711 mm)
Performance figures
Maximum speed112 1/2 mph (181 km/h)
Tractive effort30,685 lbf (136.49 kN)
Factor of adh.4.71
OperatorsMilwaukee Road
Numbers1 – 4
DispositionAll scrapped, none preserved


Milwaukee Road class A No. 1 pauses near Milwaukee in 1951.

Designed for a 6½ hour schedule between Chicago and St. Paul, the class proved capable of handling nine cars on a 6¼ hour schedule. The only change over the years, except bumps and dents in the casing, was the addition of a Mars Light beneath the winged emblem on the nose in 1947.

They hauled the fastest scheduled steam-powered trains in the world. Running at 100 mph or greater was required to keep these schedules; the class A locomotives were designed to cruise at over 100 miles per hour (160 km/h) and be able to achieve 120 mph (190 km/h). A run with a dynamometer car behind the locomotive was made on May 15, 1935, by locomotive No. 2 between Milwaukee and New Lisbon, Wisconsin. Over a 14-mile (23 km) stretch the speed of 112.5 mph (181.1 km/h) was recorded. This was the fastest authenticated speed reached by a steam locomotive at the time, making No. 2 the rail speed record holder for steam and the first steam locomotive to top 110 mph (180 km/h). There are reports, without evidence or accurate records, that these locomotives could exceed 120 miles per hour (190 km/h). Such speeds would have placed the class A in contention with the LNER Class A4 and German BR 05 for the crown of fastest steam locomotive until that time, but no records have been unearthed. The successor Milwaukee Road class F7 was even more powerful, with a claimed top speed of 125 mph (201 km/h).

The design was fairly conventional but unusual in some aspects. One goal was reducing reciprocating mass, which could not be completely balanced. This was the reason for the high boiler pressure of 300 psi (2.07 MPa), which allowed smaller pistons. Reciprocating mass of the connecting rods was also reduced with the use of four, rather than the more usual six, driving wheels. The main rods connected to the first pair of driven wheels rather than the (more conventional) second; again, this reduced the reciprocating mass as well as providing more even power throughout the stroke. The large 84-inch (2.134 m) diameter driving wheels reduced piston speed and made high speed less taxing on the machinery. The streamlined casings were designed to open easily for servicing; the front end had clamshell doors ahead of the smokebox.

Table of locomotive[1]: 32 
Road No.
serial No.
Built Retired
1 68684 May 1935 November 1951
2 68685 May 1935 November 1951
3 68729 May 1936 September 1949
4 68828 April 1937 June 1951


  • Benn, Bryan. "Fastest Steam Locomotive". Archived from the original on 2006-04-20. Retrieved 2006-01-09.
  • Ross, Don. "Chicago Milwaukee St. Paul & Pacific: Class A 4-4-2 Hiawatha Atlantics". Don's Rail Photos. Retrieved 2006-01-09.
  • Hollingsworth, Brian & Cook, Arthur (2001). The Great Book of Trains. Osceola, Wisconsin: MBI Publishing. ISBN 0-7603-1193-5.
  • Reed, Brian (1972). Loco Profile 26 - The Hiawathas. Windsor, Berkshire, UK: Profile Publications Ltd.
  1. ^ Edson, William D. (Spring 1977). "Milwaukee Road Locomotives". Railroad History. Boston, Mass.: Railway and Locomotive Historical Society. 136: 28–129. JSTOR 43523968.

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