Parallel to the five 4-4-0 with the numbers 659 to 663, the Lehigh Valley had five 4-6-0 built by Baldwin in 1895 and gave them the numbers 708 to 712. These were all Camelbacks and were nearly identical apart from the additional driving axle. They were completed by 20 other 4-6-0 with a slightly smaller boiler. The first of those also got a driver diameter of 68 inches, while the other 15 only had 62 inches.

Later when the new class scheme was adopted, they all got the prefix J, what denoted their wheel arrangement. The locomotives with 62 inch drivers were classed into class J-42, while the ones with 68 inches became class J-43. After rebuilds which changed boiler pressure and cylinder size, they were designated classes J-49 to J-52. The last ones were scrapped in 1930.

The Lehigh Valley had the ability to source large quantities of smaller fragments of anthracite coal as residues from the processing operation at less than a dollar a ton. In order to be able to use these as fuel for steam locomotives, the camelback design was used with a very wide firebox, which included a large grate area. From 1904, a larger series of ten-wheelers was produced, which were suitable for use in front of fast freight trains in the lowlands and heavy local trains.

The locomotives were designed so heavy that the axle load was just suitable for high speeds. The large firebox was a slightly modified Wootten type and did not have a combustion chamber. The load on the individual coupled axles was distributed more rear-heavy to get better traction when starting. The initial wheel diameter of 68.5 inches represented a good compromise between higher speeds and a tractive effort of more than 30,000 pounds. 

There were some changes during production, for example the wheel diameter was increased to 69 inches. While the boiler initially had 378 tubes, this number was reduced to 363 from 1907. With the exception of Baldwin's last delivery, all locomotives had Stephenson-type valve gear. Of the last Baldwin engines, eight had Walschaert valve gear and two had Baker-Pilliod valve gear.

In 1924, ALCO-Brooks built ten K-6b Pacifics for the Lehigh Valley. Their weight was between that of the K-4 and K-5, but they had the larger 77 inch drivers and the same cylinder dimensions as the K-3. Two others were rebuilt in the LV's Sayre Shops from K-3 in 1925 and 1926. In 1939 and 1940, three were streamlined with casings designed by Otto Kuhler.

The Lehigh Valley used the 4-8-4, which they dubbed “Wyoming” after the Wyoming Valley in Pennsylvania, primarily for freight trains. After one prototype each from Baldwin and ALCO, ten more were procured as T-1a and T-2a. These had the most powerful booster of all US steam locomotives in the rear bogie. The T-3 was built by Baldwin from 1934 and was also suitable for passenger trains with larger wheels. The T-2b first emerged during World War II and was derived from the T-2a. Due to the lack of material, however, this was less refined and thus weighed more heavily.