Definitely a member of the Thunderbolt family, but more powerful than even the mighty “Jug”, Republic’s XP-72 originated from design studies started even before the basic P-47 had entered service, centered around a Thunderbolt outgrowth powered by the new Pratt & Whitney X-Wasp, later the R-4360 Wasp Major.
The first of two XP-72s began flight testing in February 1944; this aircraft had a four-bladed prop, but the second had a contra-rotating unit. Performance was impressive, and production aircraft could have taken four 37mm cannon top speeds of nearly 500mph, representing a formidable capability even against such adversaries as the early Luftwaffe jets. An order for 100 P-72s was placed, but this was later cancelled as priorities shifted.
Lloyd S. Jones U.S. Fighters: Army-Air Force 1925 to 1980s p.190: XP-72 scale 3-view plans