The D&LW undertook electrification of its Morristown Line and related branches in 1929–1930, and purchased 141 motor cars from Pullman to operate it.

The service was extended in phases to other towns that would have yards to store the trains: South Orange, Summit, Gladstone, Morristown and Dover.

The MUs did travel beyond the electrified district on occasion, particularly after World War II when there was a shortage of rail cars available.

Unpowered MUs, pulled by steam locomotives, travelled on the Sussex Branch to Branchville, New Jersey, for instance, during the immediate post-war timeframe.

[1][page needed] Over the years, the distinctive Pullman green cars were considered to be extremely reliable.

Thomas T. Taber, in his book on the DL&W, called the Lackawanna MUs "...probably the finest multiple unit electric cars ever constructed."

Arrow III MU cars, which continued to run to and from Hoboken, initially replaced the Lackawanna MUs.

The introduction of Midtown Direct service to New York City in 1996, however, would prove problematic as the Northeast Corridor Line into Manhattan still used the original Pennsylvania Railroad 12,000 volt 25 hertz AC distribution system.

Given that the Arrow III cars were not engineered to easily switch from one voltage to another, it was necessary for NJ Transit to acquire new locomotives, ALP-44s, to handle the new service.

Three-car sets (two power cars plus a single coach) were used rarely, mostly as shuttle trains east of Newark, and were noted for their faster acceleration and higher top speeds, which may explain their limited use.

Outbound from Hoboken, commuters could ride on the Morristown Line (the mainline) to Dover, New Jersey, a trip of 38.3 miles (62 km).

The MUs ran off 3000 volt DC overhead electric wire, drawing current through pantographs.

[citation needed] On test runs, the trains attained a speed of 63 miles per hour (101 km/h) on level track.

[citation needed] The Lackawanna rebuilt a total of 18 combine cars for multiple unit operation: fifteen baggage/express and three railway post offices (RPO).