The design drawing for Measure 31/21D, dated March 18, 1944, for the destroyer USS Dahlgren and others. The profile used is for a 4-stack destroyer modified with two less stacks and no torpedo tubes, which was done to become a small seaplane tender (AVD).
The Design 21D pattern was derived from an earlier Measure 16 Thayer Blue pattern but used new colors. Design 21D was drawn up for USS Nashville (CL-43) as early as July 14, 1943. In late 1943 and early 1944 it was also drawn for the Fletcher class in both Measure 31 and Measure 32 colors.