The National Railway or National Air Line Railroad was a planned railroad between New York City and Washington, D.C. in the United States around 1870. Part of it was eventually built from New York to Philadelphia by the Delaware and Bound Brook Railroad and the Delaware River Branch of the North Pennsylvania Railroad, leased by the Philadelphia and Reading Railway in 1879 and becoming its New York Branch. The line was intended to provide an alternate to the various monopolies that existed along the route, specifically the United New Jersey Railroad and Canal Companies and their Camden and Amboy Railroad, and as such had a long struggle to be built.
In the spring of 1867, Henry Martyn Hamilton began planning for the National Railway between New York and Philadelphia by getting short lines chartered that would end-to-end form the complete route. The first two sections were chartered in New Jersey as the Hamilton Land Improvement Company and Millstone and Trenton Railroad, forming half of the New Jersey route. The Millstone and Trenton Railroad was authorized to build a line from Trenton northeast to Millstone, and the Hamilton Land Improvement Company could build six miles anywhere in the state, which was enough to bridge the gap from Millstone to the Central Railroad of New Jersey at Bound Brook.
The first official proposals for the railway came in 1868 at the federal level, with bills in the U.S. House of Representatives for a line between New York and Washington via Easton, Reading and Lancaster. Later proposals concentrated on the New York-Philadelphia section, and were made both at the federal level and in the states of Pennsylvania and New Jersey.