With the proposal of the U.S. Highway System in 1925, US 13 was planned as one of three routes to pass through Delaware, running from the Maryland border in Delmar via Dover and Wilmington to the Pennsylvania border in Claymont. US 13 was designated on November 11, 1926. US 13 followed the Cape Charles Route between the Maryland border in Delmar and Dover, the DuPont Highway between Dover and Wilmington, Market Street through Wilmington, and the Philadelphia Pike between Wilmington and the Pennsylvania border in Claymont. Between the Maryland border and US 40 (now DE 273) in Hares Corner, US 13 was part of the Ocean Highway, an Atlantic coastal highway stretching from Jacksonville, Florida, to New Brunswick, New Jersey, that served as the quickest route between the New York City area and Florida before the introduction of the Interstate Highway System. US 13 is one of only four U.S. Routes that form the highway and Delaware was one of the states that participated in the highway's formation.