BuNos 70188 and 70913, which were originally F6F-5 airframes, underwent conversion to become the XF6F-6 prototypes. They were equipped with the powerful 18-cylinder R-2800-18-W engine, boasting 2,100hp and featuring a two-stage supercharger and water injection system, which drove a four-bladed Hamilton Standard propeller. On July 6, 1944, BuNo 70188 took to the skies for the first time, followed by BuNo 70913. The XF6F-6 was the fastest model of the Hellcat, capable of reaching an impressive top speed of 417mph (671km/h). Despite its impressive performance, the variant never made it to mass production due to the end of World War II, resulting in its cancellation.