In the years after World War II, when short lines and industrial operators were dieselizing their operations. many of them turned to the leader in the small- to medium-size locomotive marketing, General Electric. When a medium-size locomotive was needed for switching or road units. the locomotive often chosen was the 70-ton switcher.

General Electric produced the 70-ton switcher as a complement to its 44-ton model. The idea behind the development of the 70-tonner was to provide a locomotive suitable for branch lines, switching and transfer service. To be a success, the locomotive had to satisfy certain criteria. It had to be:

• Light enough to run on 50-pound rail and light bridges,
• Powerful enough to move long cuts of cars in switching or road hauls.
and
• Fast enough to make light passenger runs.

The 44-tonner could do most of these jobs adequately, but required multiple units to pull much weight. It was evident that a new locomotive was needed - one that would be larger than the 44-tonner, but smaller than the 1,000 - horsepower types such as Alco's S-2 or the EMD NW2, The 139,000 - pound weight (70 tons) was ultimately decided on, as it would run on light trackage without necessitating major rebuilding, but could pull twice as much tonnage as the 44-ton model.

A standard end-cab layout was dictated by a decision to use the Cooper-Bessemer FWL-6T, a six-cylinder, 600-horsepower engine, instead of two smaller engines, as in the 44-tonner. This body design also provided crew protection while operating in train service, and excellent visibility for switching. Power was transmitted to the wheels using a GE GT-571 generator and four GE 748 traction motors. This combination allowed for the development of 32,600 pounds of tractive effort and a top speed of 55 MPH. In early May 1946, demonstrator 7001 was outshopped and started touring the country, displaying the unit's virtues. Short lines especially were impressed with what they saw, and ordered many units. Stories of how the 70 tonner saved a dying short line were promoted in the railway press, and General Electric took advantage of this free publicity as an opportunity to build sales.

Among the many reasons listed for the short line resurrections were:
• Little or no rebuilding of the trackage was necessary to accommodate the units,
• Up to 95 percent availability of the unit, and
• A large reduction in fuel and maintenance costs over those of steam locomotives.

As production went on, the basic layout of the unit remained unchanged, but it was upgraded cosmetically as well as mechanically. By the end of production, tractive effort had been increased to 34,100 pounds (from 32,600 pounds), top speed was 60 MPH, and the engine developed 660 horsepower compared to the initial 600 horsepower.

If we trace the development of the GE 70-ton model, the production can be divided into three distinct phases, identified by noticeable changes in the outward appearance of the locomotive.

Phase I - A70T
The A70T model was produced from 1946 to mid-1949. The first unit to use this layout was General Electric demonstrator 7001. It set the pattern for the next 175 GE 70 ton units, including export units. Two major spotting features are a single round headlight housing on each end and a flat, solid sheet steel hood front. The other major feature was a set of consecutive louvered access doors on the hood sides, generally six on the right (engineer's) side and five on the opposite side.

A70T Variations
While most of the A70T's look essentially the same, varying only with the placement of minor details such as horns and bells, a few units were specially modified for their owners. The most obvious variation was for Southwest Portland Cement. SPC's unit had a lengthened hood and more than the usual number of door louvers, necessitated by the specification of dynamic brakes and the need for extra ventilation in the harsh Mojave Desert environment. Another modification package was that applied to 50 meter-gauge units exported to Brazil in 1947. In addition to the narrow gauge, these export units rode on C-C trucks rather than the standard B-B arrangement.

Phase II - B70T
Production of the B70T phase began with Southern Pacific 5100 (builder's number 30034). SP 5100 was the first of the largest fleet of 70 tonners owned by one road, 21 units numbered 5100-5120. GE produced almost 200 units of this configuration before another design change occurred. The B70T phase represented a more modern and business-like appearance than that of the A70T version. Angles on the body were less rounded, saving on fabrication costs. The single round headlights were replaced front and rear with rectangular housings containing twin sealed beam headlights, and a louvered ventilation grille was added to the front of the hood. On the hood sides, the arrangement of louvered access doors was altered from that of the A70T. Normally, the B70T had three louvered doors followed by a solid door, then three additional louvered doors on the right side. On the left side, two louvered doors, then a solid door, followed by three more louvered doors were used. While these door patterns were standard when the units were delivered, rebuilding and customer modifications altered the appearance of the hood doors.

B70T Variations

Southwestern Portland Cement ordered a unit with the extra ventilation and dynamic braking. This resulted in a special variation of the B70T similar to SPC's A70T phase unit, but with the B70T features. Klamath Northern also ordered a similar unit with the extra ventilation, though it lacked dynamic brake and thus had the normal-length hood. Another unique variation on the B70T was ordered by Canadian National for its New Brunswick and Prince Edward Island line. CN's units had the standard B70T door arrangement, with hood end grilles, but used the older-style round headlight of the A70T. They were also equipped with lightweight trucks, similar to those found under Whitcomb's 75-ton switchers.

Phase III - C70T

The final two year of 70-tonner production gave birth to the C70T phase (domestic production ended in early 1957, so all C70T's were exported). Most noticeable in the C70T phase were the extreme angularity of construction and the absence of round comer on the hood. Louver positions remained the same as on the B70T, but instead of having the areas cut out and separate louver applied behind the openings, ventilation was provided by slits punched in the hood front and side doors. Dual sealed-beam headlights were retained, but were recessed into the body, leaving the headlight glass flush with the hood and cab end. All of these features were later incorporated into the U6B export switcher, produced in the 1960s as a replacement for the 70tonner. No C70T's were sold to U.S. Operators, but three narrow-gauge units were delivered to the Grand Falls Central in Canada and were active until sold to Nicaragua in the late 1980s.

70-ton Owners
Most orders for the 70-ton model came from short line and industrial users, but the model was no stranger to Class I railroads. Southern Pacific owned the largest fleet, 21 units, followed by Canadian National, with 18 units. In both cases, they were primarily used in low-density, light branch line service, with CN's units used in the Maritime Provinces. Other Class I purchasers included Louisville & Nashville, Missouri-Kansas Texas, and Pere Marquette. Short line operators embraced the locomotive and a brisk business soon developed in the sale of used units. Some lines, like Fort Dodge, Des Moines & Southern and Laurinburg & Southern, amassed sizable fleets of 70 tonners by acquiring used units from lines that were abandoned or bought replacement locomotives. The movement of units has been so prolific that an all-time list of 70-tonner owners is much to long to include here. Many operators, such as Modesto & Empire Traction, still depend on the 70tonner for daily use, and have undertaken an upgrading program to keep the units in top condition and to make the acquisition of repair parts easier.