The route West from Wenatchee and on to Seattle needed to cross the Northern Cascades by the Stevens Pass.

The Great Northern Railway was steam-hauled from the outset, later by diesel, and did not generally adopt electric power.

However problems with poor ventilation inside the 2.6 miles (4.2 km) long tunnel led to an early electrification scheme with four 3 phase AC boxcab locomotives, introduced in 1909.

The electrification scheme here was unusual, although not unique at the time,[i] using 3 phase AC with two overhead wires and trolley pole current collectors.

An avalanche in 1910 caused 96 fatalities to passengers and crew of a train trapped by snowdrifts at the depot of Wellington, by the West portal of the tunnel.

[3] A new tunnel was begun, longer at 7.8 miles (12.6 km), so as to avoid more of the poor winter conditions at each end.

[5] Baldwin and Westinghouse built a series of locomotives based on similar electric supplies, including a number for the New Haven Railroad.

As they were used as coupled pairs, the high voltage pantograph busbar of the two units was linked between them to give a longer connection length to the catenary wire.

[6] Regenerative braking had been used from the outset on the 3-phase boxcabs, although this had been dissipated by a load bank at the power station; with the single phase electrification, it could now be re-used by another train or fed into the supply network.

[6] Many similar four-axle Do locomotives used a switching of the motors from parallel to series or series-parallel circuits for their main control between starting and running.

The motor field could be operated as either series-wound, or with separate excitation from the generator with either a constant-current or constant-horsepower characteristics.

Post-WWII the decision was taken, in common with many of the other US electric railways operating with 1920s equipment, to convert to diesel haulage rather than to renew the electrification system.

This involved providing a closed door to the tunnel portal to control airflow, which opened automatically as a train approached.