The 3 ft (914 mm) narrow gauge railway was drawn by mules from the Andover Mine down to the Morris Canal at Waterloo Village and was then taken on to the Thomas Iron Furnaces in Allentown, Pennsylvania.

The Act by the New Jersey Legislature that incorporated the railroad also allowed for the provision of extending the rail into Newton, the county seat.

The Sussex Mine Railroad struck a deal with the M&E that would work in their favor if they were to have the connection ready for operation by the time the M&E's extension reached Waterloo.

In preparation for this extension and what eventually became a rebuilding of the entire existing line, the New Jersey Legislature approved another supplement to the charter on January 26, 1853, that allowed the company to change its name to the Sussex Railroad, reflecting its new purpose beyond just serving the mines and authorized the company to extend the track to any point in Sussex County on the Delaware River.

[1][2] The renamed Sussex Railroad Company gained support by issuing stock and bonds, which raised the necessary funds to lay the new track.

[1][2] At this point, the only stations on the Sussex Railroad were at Newton, Andover, and Waterloo, but they served many industries and moved products such as produce, dairy, meat, and of course iron ore from the mines.

This branch would allow for an outlet for Sussex County's northern agricultural products and staged the potential future expansion of the line through Culver's Gap to the Delaware River.

[1][2] At the same time as work was being done on the Branchville line, pressure was increasing to bring rail to the ever-increasing mining industries of Franklin, including the New Jersey Zinc Company.

Work finally began on this nine-mile (14 km)) extension in 1868, after a very heated debate and political power plays that could have routed traffic around Newton entirely.

Additionally, an unconnected four-mile (6.4 km) spur known as the South Vernon extension, which ran from Hamburg to McAfee, was completed in 1871 and allowed access to an iron ore mine at the base of the Pochuck mountain range via trackage rights on the New Jersey Midland Railway.

Still, there was some expansion: A new station was added at Cranberry Lake, which became a country getaway and weekend vacation spot for residents, and the Netcong-Stanhope Cutoff was completed in 1900, prompting the abandonment of the line to Waterloo.

[1][3] As industry began to decrease in the area, the rise of the automobile and trucking took away valuable passenger and freight business from the Sussex Branch.