Milwaukee Road EP-2 “Bipolars”: Specs, Production Roster & History

Last revised: August 27, 2026

The Milwaukee Road class EP-2 was a five-locomotive passenger electric built by General Electric in 1919 for the newly wired Coast Division. Railfans call them Bipolars after the motors, not after the railroad. Each of twelve driving axles carried a two-pole, gearless armature on the axle itself. The carbodies were three articulated sections on a four-piece hinged frame, AAR wheel arrangement 1B+D+D+B1. Milwaukee numbered them 10250–10254, then E1–E5 in March 1939. They were the face of the Olympian and later the Olympian Hiawatha between Tacoma and Othello for more than thirty years.

Milwaukee Road Bipolar E-3 leads the Olympian Hiawatha through Butte, Montana, winter 1958. M.L. Powell photo. American-Rails.com collection.

On this page: At a glance · Why “Bipolar” · Design · Data sheet · Production roster · Coast Division, 1919–53 · The 1953 rebuild · Mountain Division and retirement · E2 at St. Louis

At a Glance

Item	Detail
Railroad / class	Chicago, Milwaukee, St. Paul & Pacific (Milwaukee Road), class EP-2
Nickname	Bipolar / Bi-Polar
Builder	General Electric (Erie, Pa.). Serials 6978–6982. Not an Alco–GE boxcab partnership
Built / in service	1918–19 construction; regular Coast Division service 1919
Quantity	5 (the entire production; Milwaukee was GE’s only customer for the design)
Original numbers	10250–10254
1939 numbers	E1–E5 (March 1939)
Voltage	3,000 V DC overhead; dual pantographs
Wheel arrangement	AAR 1B+D+D+B1 (also written 1-B-D+D-B-1). Whyte analog 2-4-8-0+0-8-4-2
Motors	Twelve gearless bipolar motors, armature on each driving axle (~370 hp / 276 kW each)
Power	4,440 hp one-hour; about 3,180 hp continuous
Territory	Coast Division (Tacoma–Othello) 1919–1957; Mountain Division 1957–retirement
Rebuild	1953 (E5 prototype at Tacoma; E1–E4 at Milwaukee Shops)
Retired	1958–1960
Survivor	E2 (née 10251) donated 1962 to the National Museum of Transportation, Kirkwood, Mo.

Why they are called Bipolars

A bipolar motor has two field poles. On the EP-2 those poles sat in the frame beside each driving axle. The armature was pressed on the axle. There was no reduction gear, no nose-hung motor screaming in a truck. At walking speed the locomotives were almost silent. Gear growl and high-RPM motor whine simply were not there. The name is electrical, not a description of the three-piece carbody.

Gearless bipolar motors were not invented for Milwaukee. Asa F. Batchelder’s design had already appeared on New York Central S-Motors more than a decade earlier. The EP-2s were the largest application of that idea when they were new: twelve motors, twelve driving axles, one locomotive rated to take a full Milwaukee passenger train over the Cascades without a helper.

Three bodies, four frames, twelve motors

The carbody is three pieces. A short center section held the steam generator for train heat. Two longer end sections carried electrical equipment under round-topped hoods and the operator cabs. The running gear underneath is four hinged frame sections. Buff and draft went through that frame, not through the bodies. Ball-and-socket joints tied the assembly together so the locomotive could take Coast Division curvature.

Reading the AAR code: a leading idler axle at each end (the “1”), then a two-axle powered truck (B), two four-axle powered groups (D+D), another B, and the other idler. That is twelve driving axles and two guiding axles. Drivers were 44 inches; idlers 36 inches. All buffering forces ran through the locomotive frame.

They were ordered without multiple-unit control. Milwaukee wanted one motor to handle any passenger train on the Coast Division by itself. GE advertised 90 mph. The railroad rated them 70 mph, which was more than the Coast’s 60–65 mph passenger limit. Design intent, as repeated in period accounts, was a 1,000-ton passenger train on a 2 percent grade at a steady 25 mph.

Milwaukee Road Bi-Polar E-3 with the Olympian Hiawatha at Butte Montana April 27 1958

Bipolar E-3 with the Olympian Hiawatha at Butte, Montana, April 27, 1958. Photographer unknown. American-Rails.com collection.

Data sheet and specifications

Figures below follow GE / Milwaukee mechanical summaries as compiled in Middleton, Holley, and the Wikipedia/Warner digest long used for this class. Continuous horsepower is sometimes listed 3,180 and sometimes rounded to 3,200. Starting tractive effort is the 116,000 lbf figure; continuous tractive effort about 42,000 lbf.

Specification	Value
Builder	General Electric, Erie, Pa.
Builder numbers	6978–6982
Year	1919 (construction overlapping late 1918)
Type	Articulated passenger electric, 3,000 V DC
Wheel arrangement (AAR)	1B+D+D+B1
Wheel arrangement (Whyte analog)	2-4-8-0+0-8-4-2
Length (coupler pulling faces)	76 ft 0 in
Width	10 ft 0 in
Height (body / pantograph)	14 ft 11 in / 16 ft 8 in
Driving-wheel diameter	44 in
Leading-wheel diameter	36 in
Locomotive weight	530,000 lb
Adhesive weight	457,000 lb
Axle load	38,500 lb
Current collection	Dual pantograph, 3,000 V DC catenary
Traction motors	12 gearless bipolar (armature on axle), ~370 hp each
Power (one-hour)	4,440 hp (3,311 kW)
Power (continuous)	~3,180 hp (2.37 MW)
Starting tractive effort	116,000 lbf
Continuous tractive effort	~42,000 lbf
Maximum speed (railroad rating / GE claim)	70 mph / 90 mph
Train heat	Steam generator (flash boilers after 1953)
MU as built	None; added in the 1953 rebuild
Horn	Wabco E-2
Price (1919)	$200,000 each; $1 million for the five

Young lad standing next to Milwaukee Road Bipolar E-4 at Othello Washington engine terminal July 1953

A young lad stands next to Bipolar E-4 at Milwaukee’s engine terminal in Othello, Washington, July 1953—the rebuild year. American-Rails.com collection.

Production roster

Five locomotives. That is the complete class. Months of completion in secondary rosters (Diesel Shop and others) scatter from November 1918 into September 1919; GE serials 6978–6982 are the numbers that do not move. All five were rebuilt in 1953. All except E2 were towed to Seattle and cut up in 1962.

Original no.	1939 no.	GE serial	Built	Notes / disposition
10250	E1	6978	1919	Coast Division; 1953 Milwaukee Shops rebuild. Retired 1958–60. Scrapped Seattle, 1962
10251	E2	6979	1919	Same service. Donated 1962 to the National Museum of Transportation, Kirkwood, Mo. Sole survivor
10252	E3	6980	1919	Frequent Olympian Hiawatha power in 1950s photographs (Butte). Scrapped Seattle, 1962
10253	E4	6981	1919	Photographed at Othello (1953), Tacoma (c. 1954), and Deer Lodge on No. 16 (April 29, 1958). Scrapped Seattle, 1962
10254	E5	6982	1919	1953 rebuild prototype at Tacoma Shops (the one that performed). Then Milwaukee Shops did E1–E4. Scrapped Seattle, 1962

Coast Division, 1919–1953

Mountain Division electrification (Harlowton, Montana, to Avery, Idaho) had opened in 1915–16 with GE/Alco boxcabs. In 1917 Milwaukee decided to wire the Coast Division—Othello, Washington, across the Cascades to Tacoma and Seattle—and ordered the five EP-2s as the passenger motors for that plant. They cost $200,000 apiece. Wire and motors came into regular use in 1919 as USRA control of the railroads was ending.

A Bipolar could run Tacoma–Othello without a steam service stop and take grades that had needed double-headed steam. GE staged publicity tugs of war in which one EP-2 out-pulled contemporary steam. A short Mountain Division test showed them cheaper to run than the boxcabs and the Baldwin–Westinghouse Quills already on that district. They still went home to the Coast. For most of the next thirty-four years they needed no heavy rebuild. They became the image of the Olympian, and after 1947 of the Olympian Hiawatha, on Lines West.

They did not MU as a regular practice. The boxcabs did; the Bipolars usually ran as a single 76-foot motor on the point of varnish.

Milwaukee Road Bipolar E-4 with the Olympian Hiawatha at Tacoma Washington circa 1954

Bipolar E-4 with the Olympian Hiawatha at Tacoma, Washington, circa 1954—after the streamlined rebuild, still on the Coast Division. Photographer unknown. American-Rails.com collection.

The 1953 rebuild

By 1953 the five were thirty-five years old and worn from wartime traffic. Milwaukee rebuilt all of them at about $40,000 a copy: traction-motor shunts for higher speed, roller bearings, multiple-unit control, flash boilers, and a streamlined carbody. They later received the Union Pacific–inspired yellow-and-gray passenger scheme that Milwaukee used on Hiawatha power in the 1950s.

E5 was the prototype, rebuilt at Tacoma Shops, which knew electrics. It performed. The other four went to Milwaukee Shops, which did not. Electrification Department head Laurence Wylie called the Milwaukee work a poor job. His successor, T.B. Kirk, described a bundle of disconnected wires in a freshly rebuilt EP-2 tagged “We don’t know where these go.” After that the class was prone to electrical fires and failures. Tacoma spent years trying to put back what Milwaukee had undone. That is why the Bipolars last years were short.

Milwaukee Road Bi-Polar E-3 with the Olympian Hiawatha at Butte Montana October 10 1958 Richard Wallin

E-3 with the Olympian Hiawatha at Butte, Montana, October 10, 1958—Mountain Division territory, after the Coast transfer. Richard Wallin photo. American-Rails.com collection.

Mountain Division, retirement, scrap

Use dropped between 1954 and 1957. In mid-1957 the five were transferred from the Coast Division to the Mountain Division. Passenger speeds in the Rockies (over 80 mph in places) were above what the Coast had asked of them. The electrical faults followed. The EF-4 / EP-4 Little Joes, delivered around 1948–50 from a cancelled Soviet order, were already the modern mountain motors. The Bipolars were not replaced by Joes on the Coast in 1950; they were worn out, badly rebuilt, and then asked to run faster in Montana.

By 1958 the fleet was in storage; four units were subsequently towed to Seattle and scrapped in 1962, E2 withheld was for donation the same year.

Bipolar E4 on Milwaukee Road train 16 eastbound Olympian Hiawatha crew change Deer Lodge Montana April 29 1958 Richard Wallin

Crew change on train No. 16, the eastbound Olympian Hiawatha, behind Bipolar E4 at Deer Lodge, Montana, April 29, 1958. Richard Wallin photo. American-Rails.com collection.

E2 at St. Louis

E2 (built as 10251, GE 6979) was donated in 1962 to the National Museum of Transportation in Kirkwood, Missouri, and moved there that year. It has been a static exhibit ever since, shown in 1953 rebuilt form—the streamlined carbody.

Sources

Noel T. Holley, The Milwaukee Electrics (Hundman, 1999)
William D. Middleton, When the Steam Railroads Electrified (Kalmbach, 1974)
Paul T. Warner, “Locomotives of the Milwaukee Road,” Pacific Railway Journal 2, no. 6 (June 1958)
The Diesel Shop, Milwaukee Road electric motors (GE serials 6978–6982; 1939 E-numbers)
Laurence Wylie / T.B. Kirk accounts of the 1953 Milwaukee Shops rebuild, as summarized in standard EP-2 histories (Tacoma prototype vs. Milwaukee wiring)
National Museum of Transportation collection notes (E2 donation, 1962)
Jim Scribbins, The Hiawatha Story and Milwaukee Road Remembered (Olympian Hiawatha assignments)