Huh, I never knew that. I thought they were double screw UNTIL the OHP when they adopted a single screw.
The whole point throughout the postwar DE evolution was that the ships could be built in numbers and in a hurry, and traditionally the biggest bottleneck of small warship production was the cutting of main reduction gearsets. It is (or was) much easier from an industrial point of view to make one big gearset rather than two small ones, so all of the postwar DE(G)s had single screws. Note that diesels were considered too noisy for ASW operations postwar, so the fact that diesels did not require reduction gearsets was not helpful.
As time passed, it became more and more clear that these DEs could never be built rapidly in a mobilization-ship sort of sense, and any future war seemed more and more likely to be fought only with the equipment onhand. Any sort of rapid-production industrial bottleneck lost importance. However, the advent of (or prevalence of) the COGAG plant in the USN functionally required the Perry to have a single screw, as a two-turbine two-shaft plant would require one screw to be trailed for maximum economy at convoy speeds.