PRR Class Q2 No. 6194 at Crestline, OH, ca. 1940s.

(Photog. Unknown, via W. Lenheim Collection)



The Pennsylvania Railroad's class Q2 comprised one prototype and twenty-five production duplex steam locomotives of 4-4-6-4 wheel arrangement. All were built by PRR's Altoona Works.


4-4-6-4 Wheel Arrangement.

The 4-4-6-4 Wheel Arrangement. Front of locomotive at left.

(Gwernol, Public domain, via Wikimedia Commons)


Designed by Raymond Loewy, they were the largest non-articulated locomotives ever built and the most powerful locomotives ever static tested, producing 7,987 cylinder horsepower (5,956 kW) on the PRR's static test plant. They were by far the most successful duplex type. The duplex propensity to slip was combated by an automatic slip control mechanism that reduced power to the slipping unit.

The Q2 locomotive was 78% more powerful than the locomotives that PRR had in service at the time, and the company claimed the Q2 could pull 125 freight cars at a speed of 50 mph (80 km/h). These were an improved version of the previous Q1 class, which was a 4-6-4-4 dual-purpose engine instead of a 4-4-6-4 freight engine.

Despite the overall success, the Q2s were all out of service by 1951. With dieselization, they were the obvious first targets to be withdrawn since they were only a little more capable than the conventional J1 class 2-10-4s, but with far-higher operating and maintenance costs. The final Q2, 6199's power output is 7,987 hp. All have been scrapped and none were preserved.


PRR Q2 prototype No. 6131 in 1944.

(Pennsylvania Railroad, Public domain, via Wikimedia Commons)


Pennsylvania Railroad Class Q2 Overview

Type and origin
Power type: Steam
Builder: Altoona Works
Build date: 1944–45
Total produced: 26
​• Whyte 4-4-6-4
• UIC 2'BC2'
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Leading diameter: 36 in (0.914 m)
Driver diameter: 69 in (1.753 m)
Wheelbase: 26 ft 4.5 in (8.039 m) (driving); 20 ft 4 in (6.20 m) (rigid); 53 ft 5.5 in (16.294 m)
Length: 124 ft 7.125 in (37.976 m) (locomotive and tender)
Width: 11 ft 4 in (3.45 m) (storm windows open)
Height: 16 ft 5.5 in (5.017 m)
Adhesive weight: 393,000 lb (178,000 kg; 178 t)
Locomotive weight: 619,100 lb (280,800 kg; 280.8 t)
Tender weight: 430,000 lb (195,000 kg; 195 t)
Total weight: 1,049,100 lb (475,900 kg; 475.9 t)
Tender type: PRR class 180F84, 8 axles, with conductor "doghouse"
Fuel type: Soft coal
Fuel capacity: 39.86 short tons (36.16 t; 35.59 long tons)
Water capacity: 19,020 US gal (72,000 L; 15,840 imp gal)
Fuel consumption: 12.5 t (12.3 long tons; 13.8 short tons) of coal per hour; 16,600 US gal (63,000 L; 13,800 imp gal) of water per hour
Boiler: 106 in (2.692 m)
Boiler pressure: 300 psi (2.1 MPa)
Front cylinder: 19+3⁄4 in × 28 in (502 mm × 711 mm)
Rear cylinder: 23+3⁄4 in × 29 in (603 mm × 737 mm)
Valve gear: Walschaerts
Performance figures
Power output: 7,987 hp (5,956 kW) (cylinder)
Tractive effort: 100,816 lbf (without booster) / 115,816 lbf (with booster)
Factor of adhesion: 3.9
Operator: Pennsylvania Railroad
Road Numbers: 6131, 6175–6199
Last run: 1951