The Erie Class P-1 locomotives were called "triplex" locomotives because they had three sets of driving wheels. There were four such locomotives, all built by Baldwin. The Erie Railroad had three of them, the Virginian had one. Erie had a long standing custom of honoring superior engineers by painting their names on the cabs of locomotives. Triplex 5014 (originally numbered 2603) carried the name of Matt H. Shay for a number of years.

The Erie triplexes were built in 1914 and 1915. They were an attempt of the locomotive designers to put as much tractive effort as possible into one locomotive. Initially, they were numbered 2603, 2604 and 2605. They were soon renumbered to 5014 - 5016. It was said that the first triplex was capable of pulling 640 cars. However, the tractive effort that these locomotives could generate was greater than the draft gear, couplers and frames of freight cars of that era could transmit. As a result, these locomotives were used in helper (pusher) service on the "Gulf Summit" or "Susquehanna Hill" grade near Deposit NY, and were taken out of service in 1927 when the arrival of 2-8-4s on the Erie roster made 2-10-2s available for helper service. 5014 was scrapped in October 1929. All six cylinders on these locomotives were the same size. The middle set was operated at high pressure, and exhausted to the front and rear sets, both of which operated at low pressure. There was no provision for running all cylinders at high pressure.

The triplexes were used with some success on the Erie Railroad but were not without problems. They were too large for Erie's own shops. Major repairs were performed in the Lehigh Valley shops at Sayre, PA. Another major problem with the triplexes was that the steam supply was inadequate for speeds past 10mph on the Erie and 5 mph on the Virginian. Part of the problem was that the tender motor unit exhausted to the air, reducing the amount of draft available to the firebox. Another problem was the "variable adhesion" of the tender motor unit. As the coal and water was consumed, the weight on drivers was reduced, thus reducing the factor of adhesion on the tender unit.