Milwaukee Road class S3

In 1944, amidst a wartime motive power shortage, the Milwaukee Road wanted to order EMD FT diesel sets, having acquired their first four-unit set in October 1941, and their second in July 1943, but the War Production Board (WPB) only allowed them to order six more sets and prohibited them from ordering more. Instead of additional FTs, the railroad was allocated ten 4-8-4 steam locomotives from the American Locomotive Company (ALCO). These were delivered in July and September 1944, and were classified as the S3 (Nos. 260–269) by the Milwaukee Road.^[1][2]

Since the WPB has placed a moratorium on creating completely new designs, locomotive manufacturers compromised by reusing features from pre-existing designs, and ALCO drafted the S3 with features reused from other 4-8-4 classes.^[3][4]

The S3 design was similar to the Milwaukee Road's preceding Baldwin-built S2 class (Nos. 201–240) locomotives from 1937, but the frame was based from the Chicago, Rock Island and Pacific (Rock Island) R67B class, while the boiler was based from the Delaware and Hudson K-62 class.^[3] The tender, which was based from the Union Pacific FEF-1 class, was a water-bottom type with a pair of six-wheel trucks.^[5]

The 96.20 square feet (8.937 m²) of coal-burning grate supplied heat to the boiler, which was pressed at 250 psi (1.72 MPa). This supplied steam to the cylinders which had a bore of 26 inches (660 mm) and a stroke of 32 inches (813 mm). They were connected to the 74-inch (1,879.600 mm) diameter driving wheels by Walschaerts valve gear, and they were equipped with roller bearings. The S3s were also built with then-innovative mechanical devices, such as Franklin self-adjusting spring-loaded wedges and ALCO lateral motion devices.^[3] They were also equipped with an air horn.

All ten S3s were built by ALCO's Schenectady plant in July (7) and September 1944 (3). ALCO assigned order number S-1928 and serial numbers 71973 through 71982.

The S3s, along with the S2 and S1 classes, were all assigned by the Milwaukee Road as dual service locomotives, pulling both heavy freight and passenger trains.^[3] Initially, the S3s only operated east of the electrified Pacific Extension, being allocated to the Dubuque and Illinois Division (now the Canadian Pacific Kansas City Elgin Subdivision) between Chicago, Illinois and Omaha, Nebraska.^[3]

Later in service, the S3s were modified with automatic train stop systems and cab signals for passenger runs between Chicago and the Twin Cities in Minnesota. In the early 1950s, when the Korean War broke out, additional locomotives were needed to accommodate a traffic surge in the Idaho Division, so four S3s (Nos. 262, 263, 267 and 269) were converted to oil firing and sent west to work passenger and freight trains in the gap—between Avery, Idaho and Othello, Washington—in between the railroad's two electrified routes.^[1]

By March 1954, No. 260 had been transferred to the La Crosse and River Division, and No. 261 was on the Milwaukee Division; the other four coal-burners were still on the D&I Division, and the four oil-burners on the Idaho Division.^[6]

By December 1954, all the S3s were removed from service, as the Milwaukee Road was effectively dieselized.^[7] As the equipment trusts on the ten locomotives had yet to expire, they could not be scrapped or sold, so they were placed into storage – the Idaho four going to Tacoma.^[8]