Baltimore and Ohio class N-1

{{notability|date=January 2025}}{{Infobox locomotive

| name = B&O #5600 George H. Emerson

| powertype = Steam

| image = File:Baltimore and Ohio N-1 No. 5600 Locomotive at the 1939 NY World's Fair (cropped).jpg

| caption = Baltimore and Ohio Railroad #5600 George H. Emerson at the 1939 New York World's Fair.

| builder = B&O Mount Clare Shops

| builddate = May 1937

| totalproduction = 1

| whytetype = 4-4-4-4

| uicclass = 2′BB2′

| gauge = {{Track gauge|ussg|allk=on}}

| leadingdiameter = {{convert|36|in|mm|0|abbr=on}}

| driverdiameter = {{convert|76|in|mm|0|abbr=on}}

| trailingdiameter = {{convert|42|in|mm|0|abbr=on}}

| minimumcurve = 13° or {{convert|441.68|ft|m|abbr=on}} normal,
18° or {{convert|319.62|ft|m|abbr=on}} slow

| length = {{convert|117|ft|0+1/4|in|m|2|abbr=on}}

| weightondrivers = {{convert|238000|lb|kg t|abbr=in|sp=us}}

| locoweight = {{convert|386500|lb|kg t|abbr=in|sp=us}}

| tenderweight = {{convert|350000|lb|kg t|abbr=in|sp=us}}

| locotenderweight = {{convert|736500|lb|kg t|abbr=in|sp=us}}

| tendertype = Vanderbilt with two 3-axle trucks

| fueltype = Coal

| fuelcap = {{convert|46000|lb|kg t|abbr=in|sp=us}}

| watercap = {{convert|22000|usgal|abbr=on}}

| boilerpressure = {{convert|350|lbf/in2|MPa|2|abbr=on}}

| firearea = Unknown

| fireboxarea = {{convert|677|sqft|m2|abbr=on}}

| tubesandflues = {{convert|4220|sqft|m2|abbr=on}}

| totalsurface = {{convert|4897|sqft|m2|abbr=on}}

| superheatertype = B&O

| superheaterarea = {{convert|1312|sqft|m2|abbr=on}}

| cylindercount = Four, duplex

| cylindersize = {{Convert|18|x|26.5|in|mm|0|abbr=on}}

| valvegear = Walschaerts

| tractiveeffort = {{convert|65000|lbf|kN|1|abbr=on}}

| factorofadhesion = 3.66

| poweroutput = {{convert|3936|hp|kW|abbr=on}} 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 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.