"The appearance of the V-1 flying bomb, jet fighters such as the Messerschmitt Me 262, and rocket fighters such as the Messerschmitt Me 163 Komet led Republic to begin development of a high-speed variant of the Thunderbolt. Four P-47D-27-RE's were modified with a 2,800 hp R-2800-57C engine with a CH-5 supercharger and the dive brakes of the P-47D-30 as YP-47M's. An improved 13' Curtiss Electric C542S-B40 propeller was fitted, and changes were made to increase speed. These improvements raised the top speed to 473 mph. In September 1944, the last 130 aircraft from the original P-47D-30-RE order were converted into an order for a production version of the YP-47M as the P-47M-1-RE. Deliveries began in December 1944, though engine problems delayed their combat debut until a few weeks before the end of the war in Europe".
Yanks Air Museum's Thunderbolt is a YP-47M-1.
https://yanksair.org/exhibition/republi ... underbolt/Below are propeller wind tunnel tests conducted on a YP-47M.





PROPELLER BLADES USED ON P-47 AIRPLANE DURING PROPELLER TESTS