Commercial Poultry Production, by Fred Jeffrey and Dean Marble, 1955
page 54 and 56....
Delaware. The Delaware was first developed in 1940 from off colored sports which occurred in a cross between Barred Rock males and New Hampshire females. These sports lacked the inherited factor for the extension of black pigment to all parts of the plumage. which would normally have been transmitted to the progeny by the Barred Rock male. The result was a bird that was largely white but carried a slight indication of barring in the hackle, primaries, secondaries, and tail.
Many people might mistake the plumage pattern of the Delaware for that of the Columbian variety of the Plymouth Rocks, but close examination will differentiate the two patterns. In the Columbian pattern the main tail feathers are black and the white and black in the wing feathers tend to form a barring pattern. The undercolor of the Columbian pattern is a light bluish slate, whereas the Delaware carries a white undercolor.
The Delaware is classified as a dual-purpose breed but to date has made its reputation on its meat qualities rather than its egg-producing qualities. Delaware males mated with New Hampshire or Rhode Island Red females produce chicks carrying the Delaware feather pattern. When the Delaware females are mated with the New Hampshires of Rhode Islands Reds, sex-linked chicks are produced, thus giving males with the Delaware pattern and solid red females.