Faced with competition from the Pennsylvania Railroad, the New York Central planned to build a promotional high-speed express locomotive that would also be displayed at the 1893 Chicago World's Fair. With the approval of Cornelius Vanderbild II, William Buchanan developed the Class N, which was to be built in a single copy with the number 999, based on the Class I, which was already capable of speeds of around 80 mph. Although it was only a single example, it was intended to pull the “Empire State Express” between New York City and Buffalo.
Sectional drawing
Railway and Locomotive Engineering, December 1896
The magic number of 100 mph was set as the targeted top speed. The drivers were enlarged from the original 70 inches to 86 inches, which were the largest wheels on a 4-4-0 in history. The bogie and tender wheels were also enlarged to relieve the bearings at higher speeds. With the newly developed boiler, great importance was attached to a large firebox in order to increase the evaporation capacity through a direct heating surface. This was augmented by the “Water Table” developed by Buchanan, which lay in the firebox and was exposed to direct heat. Also, the boiler pressure was increased from 180 to 190 psi to partially compensate for the larger drivers.
Today's appearance with smaller wheels in the Chicago Museum
Sean Lab 
Immediately after completion in April 1893, the initially secret test runs were undertaken with four six-axle passenger cars. The controversial value of 112.5 mph was reached during the record run on May 10th. Although this was achieved on a slight gradient of 0.3 percent, a calculated boiler output of more than 2,000 hp would have been necessary with this train weight, which the boiler of the 999 could only have achieved for a brief moment. Today, the value can no longer be reliably verified, since the speeds at that time could only be determined with a stopwatch. Most likely at least 100 mph was actually achieved, while some voices assume little more than 80 mph.
After the world exhibition, the 999 was used in front of scheduled trains, whereby the low tractive effort was noticeable due to the large coupled wheels. The diameter was thus reduced first to 78 and in 1899 to 70 inches, bringing it in line with the other 4-4-0 locomotives of the New York Central. It also ended its service in front of the Empire State Express, whereupon it was used as class C-14 with a boiler pressure of only 180 psi in front of less important trains.
After initially being retired in 1924, it almost ended up being scrapped. Fortunately, since the identity of the locomotive, which was now listed as number 1086, was recognized, it was refurbished instead. It spent the time that followed with its old number again, but with the smaller wheels, at various exhibitions and special trips. In 1952 it was finally phased out, since it was now almost impossible to use a steam locomotive for advertising purposes. It was given to the Museum of Science and Industry in Chicago in 1962, where it can still be found today.