The Chicago and North Western Railway D Class was a class of 92 American 4-4-2 "Atlantic" locomotives. They were built by Schenectady Locomotive Works and by its corporate successor the American Locomotive Company between 1900 and 1908. In addition, the Chicago, St. Paul, Minneapolis and Omaha Railway (Omaha Road) bought seven, classifying them as class G-3

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Quick Facts CNW class D Omaha Road class G-3, Type and origin ...

CNW class D Omaha Road class G-3
CNW 1026, one a batch of locomotives fitted with Young valve gear and Young rotary valves.
Type and origin Power type Steam Builder Schenectady Locomotive Works American Locomotive Company Serial number see table Build date 1900–1908 Total produced 92 (CNW) 7
Specifications Configuration: ​  • Whyte 4-4-2  • UIC 2′B1′ n2 (rather 2'B1 - trailing wheels, not truck) Driver Second Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 37+1⁄4 in (0.946 m) Driver dia. 81 in (2.057 m) Trailing dia. 49 in (1.245 m) Wheelbase: ​  • Engine 26 ft 9 in (8.15 m)  • Drivers 84 in (2.13 m)  • Tender 20 ft 0 in (6.10 m)  • Tender truck 5 ft 2 in (1.575 m) Height 15 ft 1+5⁄8 in (4.613 m) over chimney Firebox: ​  • Type    • Grate area 46.22 sq ft (4.294 m2) (102 in × 65+1⁄4 in or 2.59 m × 1.66 m) Boiler: ​  • Pitch 9 ft 3 in (2.82 m)  • Diameter 68+1⁄2 in (1.74 m) Boiler pressure 200 lbf/in2 (1,400 kPa; 14 kgf/cm2) Cylinders Two Cylinder size 20 in × 26 in (508 mm × 660 mm) Valve gear Stepehenson, Young, or Walschearts Valve type Piston valves, or Young rotary valves
Performance figures Tractive effort 25,700 lbf (114.32 kN)
Career Operators Chicago and North Western Railway Omaha Road Class CNW: D CMO: G-3 (Omaha Road) Number in class CNW: 92 CMO: 7 Numbers see tables Retired 1931–1952 Preserved CNW 1015 Disposition One preserved, remainder scrapped

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The locomotives had a boiler pressurized to 200 pounds-force per square inch (1.38 MPa) providing steam to two cylinders with a 20-inch (508 mm) bore and a 26-inch (660 mm) stroke. They were connected to 81-inch (2,057 mm) driving wheels by a variety of valve gear: most had Stephenson valve gear and 11-inch (279 mm) piston valves; No. 1026 was fitted up with Youngs rotary valves and valve gear in 1903,^[1] but later reverted to Stephensons valve gear. The 1908 batch had Walschaerts valve gear, the first five locomotives having piston valves and the last ten were delivered with Young rotary valves; these were replaced with piston valves when the locomotives were fitted with superheaters.^[2]

All 92 locomotives were built by Schenectady Locomotive Works (SLW) and by the same works under its corporate successor, the American Locomotive Company (ALCO).

In September 1904, ALCO announced their introduction to steam locomotives with superheated boilers, following some successful test runs by a European locomotive at a St. Louis exhibition.^[3] The C&NW subsequently asked ALCO to construct one D class 4-4-2 (No. 1300) and one R-1 class 4-6-0 (No. 76) with superheated boilers.^[3][4] The railroad became unsatisfied with the performance of Nos. 1300 and 76, and no further D's or R-1's were built new with superheaters.^[4]

At the time of their introduction, wooden cars were the norm. The class D locomotives were quite capable of pulling a 10-car, 400-ton train on the 138-mile Chicago to Clinton route in 3 hours 25 minutes inclusive of eleven stops.^[7]

Unfortunately, steel cars came into use soon after, and the locomotives became outclassed. They were then downgraded to commuter service and locals.

On the Omaha Road, one of the later uses of their class G-3 was powering the Minneapolis to Ashland train The Namakagon substituting for the regular gas-electric car when it was in the shops or the load exceeded its two-car capacity.^[8]

Retirements started in 1931, and continued until the end of steam in 1956 when the last two were retired from Chicago commuter service.

One locomotive has been preserved: CNW 1015, the first locomotive built. It is on display at the National Museum of Transportation at Kirkwood, Missouri.