| B&O #5600 George H. Emerson | |
| Powertype: | Steam |
| Builder: | B&O Mount Clare Shops |
| Builddate: | May 1937 |
| Totalproduction: | 1 |
| Whytetype: | 4-4-4-4 |
| Uicclass: | 2′BB2′ |
| Leadingdiameter: | 360NaN0 |
| Driverdiameter: | 760NaN0 |
| Trailingdiameter: | 420NaN0 |
| Minimumcurve: | 13° or 441.68feet normal, 18° or 319.62feet slow |
| Length: | 117feet |
| Weightondrivers: | 238000abbr=inNaNabbr=in |
| Locoweight: | 386500abbr=inNaNabbr=in |
| Tenderweight: | 350000abbr=inNaNabbr=in |
| Locotenderweight: | 736500abbr=inNaNabbr=in |
| Tendertype: | Vanderbilt with two 3-axle trucks |
| Fueltype: | Coal |
| Fuelcap: | 46000abbr=inNaNabbr=in |
| Watercap: | 22000usgal |
| Boilerpressure: | 3502NaN2 |
| Firearea: | 80.5square feet |
| Fireboxarea: | 677square feet |
| Tubesandflues: | 4220square feet |
| Totalsurface: | 4897square feet |
| Superheatertype: | B&O |
| Superheaterarea: | 1312square feet |
| Cylindercount: | Four, duplex |
| Cylindersize: | 18x |
| Valvegear: | Walschaerts |
| Tractiveeffort: | 650001NaN1 |
| Factorofadhesion: | 3.66 |
| Poweroutput: | 3936hp at cylinders |
| Operator: | Baltimore and Ohio Railroad |
| Operatorclass: | N-1 |
| Fleetnumbers: | 5600 |
| Officialname: | George H. Emerson |
| Retiredate: | 1943 |
| Scrapdate: | October 1950 |
The Baltimore and Ohio Railroad's sole Class N-1 steam locomotive, #5600 (named "George H. Emerson"), was the first duplex locomotive and the first 4-4-4-4 locomotive ever built. It was unique in the fact that it had a water tube firebox, which was much larger than a normal firebox. It was designed and built by the railroad's own shops in 1937.
The rear set of cylinders were placed beside the firebox. This allowed the locomotive's wheelbase to remain the same. The space beside the firebox was hot and dirty, which caused premature cylinder wear, and the placement of the cylinders limited the size of the firebox. These same problems occurred on the PRR Q1, which also placed the rear cylinders by the firebox. It was built by the B&O's own Mount Clare Shops in 1937; however, it had problems with the sizes of the cylinders facing the other direction.
In 1943, No. 5600 was retired from service. The locomotive was then cut up for scrap in 1950.