US 113's role between Milford and Dover became secondary with the designation and extension of DE 1 throughout the state in conjunction with the proposed US 13 Relief Route, which is now the Korean War Veterans Memorial Highway from Dover Air Force Base to Christiana. DE 1 was assigned to the Milford Bypass and concurrently with DE 14 along the coastal highway south from Milford to the Maryland state line at Fenwick Island in 1973. DE 1 was co-signed with DE 14 through the Delaware beach communities until 1976, when DE 14 was truncated at Milford. The DE 1 designation was extended north by 1988 along US 113 from Milford to Dover and continuing north along US 13 toward Christiana to connect sections of the Relief Route as they were completed. In 1991, DelDOT enacted corridor preservation measures on DE 1, including its concurrency with US 113, from Dover Air Force Base to Nassau to prevent excessive development along the corridor so it can gradually be transformed into a freeway.