The first 2-6-6-4 articulated locomotive ever built was the class J-1 of the Pittsburgh & West Virginia. They were created in 1934 by Baldwin to surpass the power of existing 2-6-6-2 locomotives. In contrast to later 2-6-6-4s, the P&WV didn't need them for high power at high speed, but for heavy medium-speed freight trains in hilly terrain.

The three locomotives of class J-1 had drivers of only 63 inches (1,600 mm) and a two-axle booster in the tender that added an additional 16,000 pounds of starting tractive effort. The trailing truck allowed a Belpaire firebox with 499 square feet (46.4 m²) of heating surface and a grate of 102.3 square feet (9.5 m²).

Later the booster in the tender was removed and the drivers were enlarged to 64 inches. In 1937, four additional J-2 class locomotives were built without boosters. Even though they were not built for high speeds, they are reported to have reached speeds of 50 or 60 mph. Their retirement took place in 1953.