Milwaukee Road class A

Milwaukee Road class A
A postcard depicts the Milwaukee Road class A #2 in 1935.
Type and origin Power type Steam Builder American Locomotive Company Serial number 68684, 68685, 68729, 68828 Build date May 1935 (2), May 1936, April 1937 Total produced 4
Specifications Configuration: ​  • Whyte 4-4-2  • UIC 2′B1′ h2 Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Driver dia. 84 in (2,134 mm) Length 88 ft 8 in (27.03 m) Adhesive weight 144,500 lb (65,500 kilograms; 65.5 metric tons) Total weight 537,000 lb (244,000 kilograms; 244 metric tons) Fuel type Oil Fuel capacity 4,000 US gal (15,000 l; 3,300 imp gal) Water cap 13,000 US gal (49,000 l; 11,000 imp gal) Boiler pressure 300 lbf/in2 (2.07 MPa) Heating surface 3,245 sq ft (301.5 m2)  • Firebox 69 sq ft (6.4 m2) Superheater: ​  • Heating area 1,029 sq ft (95.6 m2) Cylinders Two Cylinder size 19 in × 28 in (483 mm × 711 mm)
Performance figures Tractive effort 30,685 lbf (136.49 kN) Factor of adh. 4.71
Career Operators Milwaukee Road Class A Numbers 1 – 4 Retired 1949–1951 Disposition All scrapped

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 in 1935-37 to haul the Milwaukee Road’s Hiawatha express passenger trains. Numbered from #1-#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 F7 "Hudsons" from 1937, they remained in top-flight service until the end. Locomotive #3 was taken out of service in 1949 and cannibalised for spares to keep the other three running until 1951. None survived into preservation.

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 mph 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 #2 between Milwaukee and New Lisbon, Wisconsin. Over a 14-mile 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 #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 mph. 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).