Although quickly replaced on the fastest trains by the larger K4s Pacifics, the E6 remained a popular locomotive on lesser services and some lasted until the end of steam on the PRR.

[5] The E6 was designed by the PRR's General Superintendent of Motive Power, Lines East, Alfred W. Gibbs, and his team.

A single prototype E6 locomotive, #5075, was turned out by the PRR's Juniata Shops in 1910; as was the railroad's standard procedure, it would undergo a thorough process of testing and experimentation before a production order was placed.

By 1910, the larger 4-6-2 "Pacific" type was the accepted express passenger locomotive, and it was somewhat contrarian for the PRR to be considering a new Atlantic class for that service.

On the PRR's static test plant at Altoona Works, the final version of the E6s produced 2,488 hp (1,855 kW) in its cylinders at 56 mph.

The tailrods were soon removed, as they were on other PRR classes that had them, and the oil headlights were replaced by electric units and turbogenerators, the latter sited between the headlamp and the stack.

As K4s Pacifics became available in greater numbers in the 1920s, the E6s locomotives were displaced from the fastest trains but continued in service in lesser assignments, and particularly along the New Jersey seashore routes.

[7] Pioneering aviator Charles Lindbergh returned to the United States on June 11, 1927, after his successful solo transatlantic flight from New York City to Paris; he was greeted by President Calvin Coolidge at Washington, D.C. and awarded the Distinguished Flying Cross.

E6s Atlantic #460 was selected, being recently overhauled but having had time to "run in" after the work; B60B baggage car #7874 was equipped as a darkroom and P70 coach #3301 would carry PRR and newsreel company officials.